Sager, W.W., Winterer, E.L., Firth, J.V., et al., 1993 Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 143

9. SITE 869l

Shipboard Scientific Party2

HOLE 869A Principal results: Site 869 (proposed Site Syl-3) is situated 45 nmi (83 km) southwest of the - pair, Pikinni Atoll (formerly Bikini) and Wode- Date occupied: 3 May 1992 jebato Guyot (formerly Sylvania). Drilling at this location was planned to Date departed: 4 May 1992 provide a basinal reference section for comparison to Leg 144 drill holes on the summit of Wodejebato and prior drilling on Pikinni. Site-survey data Time on hole: 1 day 17 hr suggested that a thick, layered succession of exists at the site that Position: ll°0.091'N, 164°44.969'E consists mainly of turbidites. Volcanic basement is not obvious in the Bottom felt (rig floor, m; drill-pipe measurement): 4837.8 site-survey seismic lines, so drilling was not expected to encounter basement . Approximately 850 m of penetration was planned, and the expecta- Distance between rig floor and (m): 11.1 tion was to bottom in volcaniclastics produced by constructional Water depth (drill-pipe measurement from sea level, m): 4826.7 volcanism on either or both Wodejebato and Pikinni. Total depth (rig floor, m): 5004.3 The location of Site 869, at 1 l°00.09'N, 164°45.02'E, was chosen on the seafloor adjacent to both Pikinni and Wodejebato, close enough to Penetration (m): 166.5 receive sediments shed mainly by these edifices, but far enough away so Number of cores (including cores with no recovery): 18 that both would contribute. It was assumed that at an adjacent basinal hole would parallel and complement that on the atoll- Total length of cored section (m): 166.5 guyot pair. For example, erosional hiatuses on the summit might be Total core recovered (m): 129.27 expected to produce sediments on the archipelagic apron, thus filling Core recovery (%): 77 "missing chapters" in the geologic history provided by summit holes. Drilling at Site 869 was undertaken to address the following primary goals: Oldest cored: Depth (mbsf): 166.5 1. Determining the history of volcanism on Pikinni/Wodejebato; Nature: Chert 2. Developing a model of Cretaceous, mid-ocean guyot/atoll Age: platform formation and evolution for the ; Measured velocity(km/s): 1.4—1.8 3. Comparison of the timing and effects of fluctuations in relative sea level among Pacific and relation to worldwide sea-level curves; and HOLE 869B 4. Deciphering the cause(s) for the drowning(s) of some Marshall Islands guyots (such as Wodejebato) vs. the existence of Cenozoic reefs Date occupied: 4 May 1992 on nearby (such as Pikinni). Date departed: 15 May 1992 Time on hole: 10 days 20 hr Two holes were drilled at Site 869, an APC/XCB hole (Hole 869A), and an RCB hole (Hole 869B), the latter located about 93 m north of the Position: ll°0.093'N, 164°45.019'E former. The operational plan was to use the APC/XCB combination to Bottom felt (rig floor, m; drill-pipe measurement): 4837.8 obtain relatively undisturbed cores from the upper 300 to 400 m of the sedimentary column. In analogy to Site 462, hard chert layers were Distance between rig floor and sea level (m): 11.1 expected to frustrate drilling at about 300 to 400 mbsf, and a round-trip Water depth (drill-pipe measurement from sea level, m): 4826.7 was planned to change to an RCB bit and begin a second hole. Chert and Total depth (rig floor, m): 5634.0 porcellanite were encountered at much shallower depths than expected, and Hole 869A was terminated at a depth of only 166.5 mbsf. Hole 869B Penetration (m): 796.2 was washed to 140.0 mbsf and cored continuously to a total depth of Number of cores (including cores with no recovery): 69 796.2 mbsf. Total length of cored section (m): 796.2 Core recovery in Hole 869A, drilled with the APC/XCB combination, was mostly excellent, with the average being over 100% for the APC cores Total core recovered (m): 252.04 and 77.6% overall. In Hole 869B, recovery was variable (see "Operations" Core recovery (%): 31 section, this chapter). In cherty sections, recovery was generally low, and Oldest sediment cored: we obtained only a few pebbles of chert in some cores. In contrast, recovery Depth (mbsf): 796.2 in Cretaceous volcaniclastic turbidites was typically in excess of 60%. In general, recovery increased downhole in Hole 869B, averaging about 20% Nature: Volcanic from 200 to 500 mbsf and increasing to 70% at the bottom of the hole. Age: Cenomanian Measured velocity (km/s): 3.0^.0 Using combined microfossil and macrofossil biostratigraphy, visual core descriptions augmented with smear-slide and thin-section data, physical properties data, and downhole logs, three principal stratigraphic units were recognized (see "Lithostratigraphy" section, this chapter). In ' Sager, W.W., Winterer, E.L., Firth, J.V., et al., 1993. Proc. ODP, Init. Repts., 143: College Station, TX (Ocean Drilling Program). stratigraphic order, from bottom to top, the lithologic divisions are de- " Shipboard Scientific Party is as given in list of participants preceding the contents. scribed as follows:

297 SITE 869

1. Unit III (796.2-207.7 mbsf> Middle-upper Cenomanian to upper panian section, from approximately 400 to 225 mbsf. Poor recovery Campanian-lower Maastrichtian volcaniclastics interlayered with nanno- prevents the dating of the interval from 225 to 207 mbsf, but this interval and radiolarian claystone. This unit is characterized by numerous gray resembles the Cretaceous volcaniclastic section in downhole logs. Into the to green volcaniclastic and intercalated with lighter- Cenozoic, lithology changes to cherts and radiolarian-nannofossil oozes. colored claystones. Seven lithologic subunits can be recognized on the basis The uppermost cored interval of Hole 869B is early to early of changes in the mix, grain sizes of, or depositional style of the dominant Eocene in age. Hole 869A yielded entirely Cenozoic sediments that range components. Subunits IIIF (780.7-653.3 mbsf), HIE (653.3-536.1 mbsf), in age from middle Eocene to early . The stratigraphic progression and IIIC (487.8^58.8 mbsf), and III A (381.5-207.7 mbsf) consist mostly at Site 869 is punctuated by five recognized hiatuses. The missing strata of volcaniclastic sandstone interbedded with claystone. These similar sub- are (1) the upper Coniacian to lower Santonian; (2) upper Maastrichtian to units are punctuated by Subunits IIIG (796.2-780.7 mbsf), a volcanic lower Paleocene; (3) part of the upper Paleocene; (4) a section including siltstone with calcareous claystone, Subunits HID (536.1^87.8 mbsf), a the /Miocene boundary; and (5) post-early Miocene age sedi- volcanic , and IIIB (458.8-381.5 mbsf), which consists mainly of ments missing at the seafloor. Of these, the most prominent is the upper radiolarian-rich claystone. Maastrichtian-lower Paleocene hiatus, which spans up to 10 m.y. and The volcaniclastic layers consist mainly of sand-size grains, deposited includes the Cretaceous/Tertiary boundary. as turbidites. Basaltic clasts are common, in places forming breccias, but Paleomagnetic measurements of the sediments cored in Hole 869A were also occurring within a fine-grained matrix and implying transportation by ruined by pervasive rust contamination of the APC/XCB cores. Measure- grain flow. Most clasts are subangular to subrounded, suggesting a moderate ments of discrete samples and archive-half samples from the Cretaceous transport distance. The largest clasts are up to 80 mm in diameter, and most section of Hole 869B showed normal polarity down to Core 143-869B-21R, have been affected by light to moderate alteration. The volcaniclastic layers reversed polarity from Cores 143-869B-21R to -26R, and normal polarity contain clinopyroxene, palagonite, feldspar, , epidote, and chlorite below. This reversed zone has been interpreted as Chron 33R, the first grains, attesting to a basaltic parentage. are a common cement. reversed polarity epoch after the Cretaceous Quiet Period (Cretaceous Long Claystones occur abundantly in some parts of the section (e.g., Sub- Normal Superchron, K-N). Paleolatitudes from Hole 869B samples are in unit IIIB), but rarely in others (e.g., Subunit IIIF). They are locally calcare- low southern latitudes, 10°-20°S. ous, siliceous, and/or zeolitic. Radiolarian and nannofossil concentrations Because shipboard magnetic interpretations were ham- are variable; in some layers, these are dispersed through the matrix pered by rust contamination in Hole 869A and by the few reversals in the and in others they are concentrated in millimeter-scale beds. Within the Cretaceous sections drilled in Hole 869B, calculated sedimentation rates Cenomanian section, unequivocal shallow-water debris are absent. Shal- were based solely on biostratigraphy. Sediments accumulated in the Ceno- low-water biogenic fragments occur only rarely in the Turanian to Maas- manian section, from the bottom of the hole up to about 470 mbsf, at the trichtian beds above, mainly in Subunits IIIA, IIIB, and IIIC. Bivalve shell, rapid rate of 60 m/m.y. or greater. In the Cretaceous section above, up to a gastropod, echinoid, red-algal, and recrystallized skeletal fragments were depth of about 207 mbsf, the overall rate was about 15 m/m.y. A hiatus of found as were orbitoid foraminifers, micritic ooids, peloids, and glau- 10 m.y. duration may separate the Cenozoic and parts of the conite. Coalified woody fragments were found in Core 143-869B-51R, at sedimentation curve. The average sedimentation rate in the Cenozoic was a depth of 618 mbsf. about 4.5 m/m.y. 2. Unit 11(166.5-88.2 mbsf, Hole 869A; 207.7-140.0 mbsf, Hole 869B). Marked downhole concentration trends of cations reflect diagenetic Lower Paleocene to upper Eocene radiolarian-nannofossil ooze and nanno- changes within the volcanogenic sediments: Ca and Sr are released by fossil-radiolarian ooze with porcellanites and chert. Recovery of this unit feldspars, whereas Mg, K, Na, and Rb are decreased by incorporation into was low, but it appears to consist of alternating layers of hard chert and soft alteration products. High silica concentrations in Hole 869A result from ooze. Porcellanites and cherts make up a significant fraction of the recovered high biogenic silica concentrations. CaCO3 percentage varied with the mix lithology in the bottom of the unit and decrease in abundance upward. Layers of sedimentary components, from high values of greater than 97% to low of nannofossil and chalk occur in places through the section. values of less than 1 % in some cherts, claystones, and volcaniclastic layers. 3. Unit I (88.2-0.0 mbsf, Hole 869A). Upper Eocene to lower Miocene In Hole 869A, CaCO3 increases with depth from about 50% in lithologic clayey nannofossil ooze and radiolarian-nannofossil ooze. Major compo- Subunit IA, is nearly constant above 90% in Subunit IB, and then decreases nents of the oozes are nannofossils, radiolarians, sponge spicules. and . with depth to about 20% at the bottom of Unit II. In Hole 869B, CaCO3 Color and compositional changes show cycles, on various scales, as the concentration is highly variable, but generally low, typically less than 10%. mix of principal components varies. The unit is divided into two subunits Peaks of CaCO3, commonly greater than 20%, occur commonly within by a stratigraphic gap between the upper Oligocene and lower Miocene. chalk and claystone layers intercalated between volcanogenic layers. TOC in both Holes 869A and 869B is low to very low, with the greatest values Nannofossils provided most of the datable biomarkers for constructing less than 0.8%. an age framework for Holes 869A and 869B. Abundance increases uphole, Overall, physical-property trends at Site 869 are what one would expect from few to absent in the volcaniclastic turbidites to abundant in the ooze for basinal sediments: bulk density and sonic velocity increase slightly section. Preservation is generally moderate to poor. Foraminifers are few to downhole (from about 1.5 to 2.1 g/cm3 and 1.5 to 2.6 km/s), whereas rare and also generally increase in abundance uphole in the upper Cretaceous porosity and water content decrease (from 70% to 35% and 60% to 20%, section; however, they are missing from all but the Oligocene of Hole 869A. respectively). Superimposed upon these trends are fluctuations caused by Their preservation is typically poor. Radiolarians are common, but no variations in the composition and layering of turbidites and volcanic specialist was on board this ship to study them, so these did not contribute breccias. The radiolarian and nannofossil-rich oozes of Hole 869A show to the shipboard biostratigraphy. remarkable variations in bulk density, apparently owing to variable car- The lower portion of Hole 869B consists of about 320 m of intercalated bonate content; nevertheless, the sonic velocity remains nearly constant turbidites and claystones of late Cenomanian age. Extremely rapid sedi- throughout, except for the intercalated chert layers. Physical properties are mentation rates are indicated, as virtually the entire Cenomanian sequence more variable in cores from Hole 869B than in those from Hole 869A is within the upper two Cenomanian nannofossil biozones, CC10 and CC9. because the former have highly variable compositions that consist mostly Foraminifers suggest a potentially greater time span, with most of the of volcaniclastic turbidites and breccias interlayered with marly, nannofos- Cenomanian strata being within the upper Cenomanian, except the deepest sil- and radiolarian-rich claystones. Sonic velocities as high as 4 to 5 km/s cores, which may be from the middle Cenomanian. and anisotropies of more than 15% were measured from samples of cores Above the Cenomanian strata (up to 207.7 mbsf), more volcaniclastic from the lower 300 m of Hole 869B. turbidites and intercalated claystones range in age from Turanian to late Four logging runs were conducted in Hole 869B. The first, using the Campanian/early Maastrichtian. This interval contains an expanded Cam- quad-tool (gamma-ray, sonic-velocity, neutron-porosity, resistivity, and

298 SITE 869 temperature), extended from 777 mbsf to the drill pipe at 112 mbsf. For BACKGROUND AND SCIENTIFIC OBJECTIVES the second and third runs (the formation microscanner [FMS] and Japanese magnetometer), hole-penetration problems dictated lowering the pipe to Site 869 (proposed site Syl-3), located at 1 l°00.09'N, 164°45.02'E 235 mbsf, below the Cenozoic chert layers. The FMS and magnetometer in water 4827 m deep, was drilled in the basin approximately 40 nmi were then lowered to 775 and 724 mbsf, respectively, and run up to the (74 km) southwest of the dumbbell-shaped volcanic edifice consisting base of the pipe. The final run, with the geochemical tool string, was of Wodejebato Guyot (formerly Sylvania) and Pikinni Atoll (formerly abbreviated because of time constraints, but it recorded data from 560 to Bikini) in the northern Marshall Islands (Fig. 1). Although they have 360 mbsf. foundations on the same volcanic edifice, Pikinni is a modern, living The quad-tool produced good data that showed excellent correlation atoll, whereas Wodejebato has drowned. Drilling at Pikinni docu- of resistivity, density, and gamma-ray reflectance with lithology and the mented that a shallow-water has existed there seismic reflection record. In particular, several prominent volcaniclastic since Miocene time (Cole, 1954; Schlanger, 1963) and by analogy to turbidite-breccia layers show up as fining-upward sequences. The Japa- Anewetak, perhaps since Eocene time (Schlanger, 1963). Presumably, nese magnetometer showed prominent anomalies that also correspond to Pikinni and Wodejebato share a similar early history, but it is a mys- some of these units. Interpretation of the FMS and geochemical tool data tery why the Pikinni platform grew, when Wodejebato drowned. await processing, but the preliminary FMS data, in particular, promise a The purpose of the site was to sample the distal part of the good record of the structure of the borehole wall. archipelagic apron shed into the basin from the nearby atoll and guyot. Combining downhole sonic velocity logs with lithologic and physical This site is complementary to proposed Leg 144 sites on the summit properties data, changes in acoustic impedance can be determined that of Wodejebato Guyot, as Site 463 was to the summit holes (866-868) correlate with most seismic reflectors. In general, the Cenozoic layers drilled on Resolution Guyot. Not only will the core material help to show hummocky forms that suggest turbidite channels, and strong reflec- define the history of volcanic and carbonate-platform growth events, tors appear to be caused by silicified layers of porcellanite or chert. The but the patterns of redeposition possibly carry a signal from sea-level upper Mesozoic layers appear more flat-lying, and reflectors come in fluctuations. Site 869 data also provide a comparison with results packets that probably were caused by volcaniclastic turbidites. The strong- from two other nearby basinal sites near guyots: Site 462 in the Nauru est and most continuous reflector, at a two-way traveltime of 0.44 s, Basin (Larson and Schlanger, 1981) and Site 585 in the East Mariana appears to correlate with the sharp base of a unit of coarse volcanic breccia Basin (Moberly, Schlanger, et al., 1986). and turbidites cored from 509 to 543 mbsf. Reflectors beneath this depth Seismic reflection data collected during site surveys (see "Site become increasingly intermittent and indicate more relief, corresponding Geophysics" section, this chapter) show multiple reflections within to massive volcaniclastic turbidites and breccias of the rapidly deposited about 1.055 two-way traveltime of the seafloor. Although the ages of Cenomanian section. Drilling at Site 869 terminated at a depth of the reflectors were not known, it was assumed that they represented 796.2 mbsf, short of at least two additional reflectors at two-way trav- most of the history of the nearby guyot and atoll: possible Early eltimes of 0.89 and 1.05 s, with extrapolated depths of 1000 and 1230 mbsf. Cretaceous volcanism and carbonate platform initiation, middle to Nothing in the seismic records indicates true basaltic basement, which Late Cretaceous volcanism, and (and Paleocene?) carbonate suggests that the sedimentary section at Site 869 may be thick. platform sediments from Pikinni (Cole, 1954; Schlanger, 1963). The Site 869 shows rapid deposition of Cretaceous sediments, mainly depth to volcanic basement was also uncertain because there was no volcaniclastic sandstones, siltstones, and breccias, against a background clear, strong seismic reflector that could be interpreted as the bottom of pelagic sedimentation. A thick section of Cenomanian volcaniclastics, of the sediment pile. Consequently, drilling at Site 869 was not over 300 m in thickness, was cored from the bottom of Hole 869B, and no intended to reach oceanic basement. Instead, a hole 850 to 1000 m bottom was reached. This suggests that volcanism on nearby deep bottoming in volcaniclastics formed during the initial volcanism (probably Wodejebato or Pikinni) contributed a large volume of material of the guyot pair was envisaged. to the adjacent basin. Interestingly, dredges from nearby Wodejebato Guyot yielded Albian shallow-water , implying that the under- Site Selection lying formed during or prior to the Albian, a chapter of the depositional history not sampled at Site 869. Site 869 was chosen at a spot some distance from Wodejebato/ The Cenomanian section is nearly devoid of shallow-water material, Pikinni so that the most continuous and complete record of the edifice suggesting that the massive influx of volcaniclastics overwhelmed any evolution could be cored. A site closer to the feature would possibly influx of such material. Conversely, higher in the section, shallow-water obtain larger sedimentary grains, but at the risk of having some debris becomes more abundant, although it is still rare. Volcaniclastic sediments bypass the site. The older sedimentary layers may onlap material waxed and waned through the rest of the Cretaceous, with a the flank of the volcanic pedestal and may not be present close to the significant influx during the early to late Campanian, perhaps signaling feature. Furthermore, seafloor topography and seismic reflection another phase of volcanism on a nearby seamount. Campanian-Maas- records suggest that turbidite channels have criss-crossed the territory trichtian shallow-water fossils have been dredged from the summit of between the site and the edifice; thus, closer sites might miss portions Wodejebato Guyot (see "Background and Objectives" section, this chapter), of the sedimentary record because some turbidites might be deflected. implying that it had built up into shallow water at that time. Grain sizes and Seismic lines over Site 869 and in the vicinity show that the layers distributions vary greatly in the volcaniclastic layers. Coarse-grained brec- are relatively flat-lying, with only a very slight slope (0.3°) upward cias (with clasts up to 80 mm in diameter), sand and silt-grade turbidites, toward the Wodejebato/Pikinni edifice. Consequently, the exact po- and grain-flow deposits having large clasts surrounded by fine-grained sition of the site was not critical. Pre-drilling seismic profiles showed matrix can be seen. These imply energetic, probably channelized, transport no surprises, so a positioning beacon was dropped as close to the by turbidite, grain, and mass flows from relatively nearby sources. proposed site location as possible (see "Operations" section, this At the end of the Cretaceous, the volcaniclastic sedimentation waned chapter). The proposed location was ll°00.00'N, 164°45.00'E and and pelagic sedimentation prevailed, beginning with nannofossil and radi- the actual position was ll°00.09'N, 164°45.02'E. olarian-rich oozes, some of which were silicified into chert and porcellanite layers. Sedimentation was episodic, with numerous hiatuses and low Geologic Background sedimentation rates during the Cenozoic. Many of the Cenozoic sedimen- tary layers are turbidites, probably shed from the nearby Wodejebato- Site 869 is within the Marshall Islands province, a group of atolls, Pikinni edifice. Sediments younger than early Miocene are not present at guyots, and seamounts in the western central Pacific Ocean situated Site 869, and the seafloor morphology in 3.5-kHz records suggests that between the Mid-Pacific Mountains and the Ontong-Java Plateau. they have been removed, probably by bottom currents. The seamounts stand on abyssal seafloor, 5500 to 5000 m deep, and chains are approximately perpendicular to the mag- 50 netic lineations and occur near lineation offsets, suggesting that they formed by volcanism along fracture zones (Larson, 1976). Site 869

Drilling Objectives These data will be compared with the results of drilling on the sum- mit of the guyot by Leg 144 as well as data from other Leg 143 and The general goals of drilling at Site 869 were as follows: 144 sites. A paleolatitude history, Objective 4, will be the result of detailed 1. To develop a history of Cretaceous mid-ocean carbonate plat- shore-based studies of the of core samples from form growth and evolution by determining the lithologic, biostrati- Site 869. Because the sediments have ages spanning much of the graphic, isotopic, and seismic stratigraphic succession within the history of the guyot/atoll pair, it should be possible to examine paleo- sediment apron adjacent to a guyot/atoll pair for latitude trends for implications of the tectonic drift history of the A. Correlation of cores and seismic records with other guyots edifice and the Pacific Plate. drilled during Legs 143 and 144; and Carbonate-platform biotic assemblages (Objective 6) will be stud- B. Comparisons of the timing and effects of changes in relative ied by microscopic and macroscopic examinations of carbonate de- sea level among Pacific guyots and world-wide sea-level curves; bris contained within the redeposited sediments. The fossil content 2. To decipher the volcanic history of the Wodejebato/Pikinni edifice; will be compared with the known ranges and ages of Cretaceous 3. To determine the cause(s) for the drowning(s) of the platform carbonate-platform biota. on Wodejebato and the reason for the existence of the Pikinni reefs The of deep-sea sediments (Objective 7) will be ad- during Cenozoic time. dressed by detailed petrographic examination of thin sections, com- bined with petrologic and isotopic analyses of rock compositions. Because Site 869 is located on deep seafloor, rather than the top Downhole logs will be used for additional information about compo- of the guyot, scientific goals were not restricted to carbonate-platform sition and stratigraphic framework. Other properties, such as paleo- objectives. Some specific Site 869 objectives are as follows: magnetism, may also yield information cogent to this problem. Objective 8, pore-water geochemistry, was accomplished by ana- 4. To calculate paleolatitudes for constraining the tectonic history lyzing interstitial waters squeezed from whole-round samples taken of the Marshall Islands and Pacific Plate; from softer sediments and from crushed sedimentary rock fragments. 5. To refine the magnetic polarity reversal time scale for the Early Objective 9, the derivation of velocity and density vs. depth curves to Late Cretaceous; for seismic interpretation, was attacked from several directions. One 6. To compare carbonate-platform biotic assemblages with others tack was to obtain downhole logs of in-situ sonic wave velocity and of similar age elsewhere as a clue to migration patterns; density. Another was to perform complementary measurements for 7. To study the diagenetic history of deep-water sediments; the recovered cores. In addition, a seismic refraction line was shot 8. To gather pore-water samples as a means of inferring residence across Site 869 using an expendable sonobuoy (see "Operations" times and chemical evolution of interstitial waters; section, this chapter). 9. To determine seismic wave velocities in Cretaceous to Tertiary Once again, downhole logs (Objective 10) proved to be extremely deep-sea sediments for use in interpretation and correlation of seismic valuable for reconstructing the stratigraphy of Site 869. Not only did reflection and refraction data; and these provide a framework for understanding partial core recovery, 10. To obtain a suite of downhole logs that would illuminate the they contributed continuous downhole data sets of physical and structure, stratigraphy, and composition of deep-sea sediments in the chemical properties that were used to see general trends in the vicinity of atolls and guyots. sediments. Geophysical (sonic velocity, spectral gamma-ray, bulk density, resistivity, and porosity) and geochemical strings were run to Objectives Addressed and Accomplished measure in-situ physical properties and compositional variations. Downhole magnetic field data were obtained with the Japanese As outlined in the sections of this chapter, preliminary shipboard magnetometer to record volcanic layers and their magnetic properties. study of core samples and downhole logs collected at Site 869 suggest In addition, the FMS was used to map resistivity variations in the that the main scientific objectives can be met through further post- borehole wall to provide a picture of structure and bedding. cruise study of the data and samples. Core recovery was mostly good to excellent, amounting to nearly 100% in the APC and XCB cores OPERATIONS of Hole 869A, and typically 15% to 40% in the RCB cores of Transit from Site 868 Hole 869B. Recovery decreased significantly, to less than 5%, when chert layers were encountered, but the downhole logs were particu- After completing the exit survey over Resolution Guyot upon larly helpful for filling the gaps. leaving Site 868, the ship turned on a course toward proposed The first, stratigraphic set of objectives was addressed by detailed Site Syl-3, now Site 869, in the basin immediately west of Wodejebato examination of lithology and fossil content of the cored sediments. (formerly Sylvania) Guyot and Pikinni (formerly Bikini) Atoll, in the Shipboard age data from microfossil studies are preliminary and must central part of the Marshall Islands Chain. We made slight deviations be adjusted for possible time lags caused by redeposition; neverthe- in the ship's course to Site 869 to obtain seismic-reflection and less, they place strong constraints on the ages of the sediments and magnetic data from several poorly surveyed guyots that lie close to seismic reflectors as well as the timing of events. Additional age the great circle route to Site 869. One of these guyots was Wodejebato constraints will become available through post-cruise strontium-iso- Guyot, which was scheduled for drilling during Leg 144 (see "Un- tope measurements in core samples. derway Geophysics" chapter, this volume). Determining the volcanic history of the Wodejebato/Pikinni edi- fice (Objective 2) will be addressed by obtaining dates for redeposited Approach to Site 869 volcaniclastic sediments. Ages for the volcaniclastic grains come from direct 40Ar-39Ar radiometric dating. Furthermore, biostrati- After terminating the pass over Wodejebato Guyot, the ship re- graphic and isotopic dates will help when constraining age. These sumed its normal speed of about 10.5 kt until arriving at a point about dates will be used with magnetic polarity measurements to address 10 nmi (19 km) northeast of Site 869, where the ship slowed to 6 kt Objective 5, refining the magnetic polarity reversal time scale. to obtain good-quality seismic-reflection data and a sonobuoy refrac- Objective 3, determining the cause(s) of drowning for the car- tion line over the proposed site. The first expendable sonobuoy was bonates atop Wodejebato, will be pursued by a study of the types, deployed, but failed after about half an hour. A backup sonobuoy was ages, and compositions of carbonate sediments shed by the edifice. deployed, but because the ship was now only 2.5 nmi (4.5 km) from

301 SITE 869

the site, the refraction line was extended. At about 6 nmi (11 km) past acoustic basement (estimated to be at a depth of about 900 mbsf), and the site, the signal faded, but not before a good wide-angle refraction reentering the hole using a minicone should the first bit not last. profile with several refractors was obtained (see "Underway Geo- Hole 869A was spudded in at about 0230 UTC, 3 May 1992, and physics" chapter, this volume). an APC core, Core 143-869A-1H, taken from 4837.8 to 4847.5 m The geophysical gear was hauled aboard, and the ship turned to below the rig floor. When retrieved, the core barrel was seen to be go back to the proposed site. The seismic reflectors at Site 869 are full, and the depth to the seafloor (from the derrick floor) was accepted relatively flat-lying; thus, little was to be gained by adjusting the site as 4837.8 m. This compares with the 4842.4-m depth predicted from location. Therefore, an acoustic beacon was dropped at 1935 UTC, the PDR. 2 May, at the proposed Syl-3 location. This beacon gave an erratic Coring proceeded (Table 1) with the APC system without diffi- signal, so after the ship was on location, this first beacon was released culty and with complete recovery down to a depth of 85.7 mbsf and recovered and another beacon dropped in its stead. (Fig. 2). Core 143-869B-10H returned empty and with the piston rod sheared. It appeared that the core barrel had hit a hard layer and Coring Operations at Hole 869A stopped, but the pressure behind the APC broke the rod. Because the resistance of the sediments to coring was increasing, we elected to A bottom-hole assembly (BHA) was assembled for use with the use the XCB system and because the interval of the core had not APC/XCB coring system. The plan was to go as far as possible with actually been drilled, the XCB was used to drill through the same this coring method in Hole 869 A and then to trip out and run in interval. It returned with 2.7 m of core, including a hard chert layer Hole 869B with the RCB system, washing through most of the more than 10 cm thick. We then cored ahead to 165.5 mbsf in Eocene interval cored with the APC/XCB in the previous hole, and then pelagic sediments that contained a few small fragments of porcel- coring ahead. The plan envisioned using a rotary bit all the way to lanous chert (Fig. 2). Between 165.5 and 166.6 mbsf, while trying to

Table 1. Coring summary for Holes 869A and 869B.

Date Length Length Date Length Length Core (May Time Depth cored recovered Recovery Core (May Time Depth cored recovered Recovery no. 1992) (UTC) (mbsf) (m) (m) (%) no. 1992) (UTC) (mbsf) (m) (m) (%)

143-869 A- 25 R 6 1800 362.2-371.8 9.6 4.00 41.6 26R 6 2030 371.8-381.5 9.7 1.65 17.0 1H 3 0330 0.0-9.7 9.7 9.69 99.9 27R 7 0000 381.5-391.1 9.6 0.70 7.3 2H 3 0445 9.7-19.2 9.5 9.84 103.0 28R 7 0200 391.1^00.8 9.7 0.16 1.7 3H 3 0540 19.2-28.7 9.5 9.83 103.0 29R 7 0350 400.8^10.4 9.6 0.19 2.0 4H 3 0630 28.7-38.2 9.5 9.76 103.0 3 OR 7 0600 410.4^20.1 9.7 0.26 2.7 5H 3 0725 38.2-47.7 9.5 9.92 104.0 31R 7 0905 420.1^29.8 9.7 2.16 22.2 6H 3 0820 47.7-57.2 9.5 9.94 104.0 32R 7 1130 429.8^39.4 9.6 3.32 34.6 7H 3 0920 57.2-66.7 9.5 10.17 107.0 33R 7 1400 439.4-449.1 9.7 1.68 17.3 8H 3 1020 66.7-76.2 9.5 10.12 106.5 34R 7 1620 449.1^58.8 9.7 3.53 36.4 9H 3 1120 76.2-85.7 9.5 10.01 105.3 35 R 7 1915 458.8^68.4 9.6 0.98 10.2 I0X 3 1405 85.7-95.5 9.8 2.72 27.7 36R 7 2130 468.4-478.1 9.7 5.38 55.4 1IX 3 1455 95.5-105.5 ]().() 7.15 71.5 37R 7 2320 478.1^87.7 9.6 0.29 3.0 12X 3 1555 105.5-115.5 10.0 7.34 73.4 38R 8 0245 487.7^97.4 9.7 3.79 39.1 13X 3 1800 115.5-125.5 ]().() 6.38 63.8 39R 8 0550 497.4-507.1 9.7 2.99 30.8 14X 3 1900 125.5-135.5 10.0 7.75 77.5 40R 8 0945 507.1-516.8 9.7 3.68 37.9 15X 3 2030 135.5-145.5 !().() 8.38 83.8 41R 8 1340 516.8-526.4 9.6 6.52 67.9 16X 3 2230 145.5-155.5 10.0 0.22 2.2 42R 8 1645 526.4-536.1 9.7 5.18 53.4 17X 4 0000 155.5-165.5 10.0 0.05 0.5 43 R 8 2130 536.1-545.6 9.5 2.51 26.4 18X 4 0200 165.5-166.5 1.0 0.00 0.0 44R 9 0145 545.6-555.3 9.7 7.24 74.6 9 45R 0530 *J.J*J555 3. _»— 56JUT.4 6U 9.3 6.80 73.1 Coring totals 166.5 129.27 77.6 46R 9 0825 564.6-574.3 9.7 0.80 8.3 47R 9 1035 574.3_583.9 9.6 0.04 0.4 143-869B- 48R 9 1420 583.9-593.5 9.6 0.81 8.4 49 R 9 1715 593.5-603.2 9.7 0.27 2.8 1\V 4 2330 0.0-140.0 140.0 9.54 (wash core) 50R 9 2245 603.2-612.7 9.5 8.99 94.6 2R 5 0110 140.0-149.6 9.6 0.50 5.2 51R 10 0145 612.7-622.4 9.7 8.41 86.7 3R 5 0215 149.6-159.3 9.7 0.09 0.9 52R 10 0400 622.4-632.0 9.6 8.09 84.3 4R 5 0400 159.3-168.9 9.6 0.64 6.7 53R 10 0720 632.0-641.8 9.8 5.55 56.6 5R 5 0520 168.9-178.6 9.7 1.08 11.1 54R 10 1340 641.8-651.5 9.7 8.56 88.2 6R 5 0645 178.6-188.3 9.7 0.27 2.8 55 R 10 1700 651.5-661.2 9.7 6.82 70.3 7R 5 0810 188.3-197.9 9.6 0.28 2.9 56R 10 2000 661.2-670.7 9.5 4.69 49.3 8R 5 0955 197.9-207.6 9.7 0.12 1.2 57R 10 2315 670.7-680.4 9.7 6.40 66.0 9R 5 1120 207.6-217.2 9.6 0.10 1.0 58R 11 0230 680.4-690.0 9.6 7.95 82.8 10R 5 1240 217.2-226.9 9.7 2.24 23.1 59R II 0530 690.0-699.7 9.7 8.33 85.9 11R 5 1405 226.9-236.6 9.7 6.42 66.2 60R II 0840 699.7-709.4 9.7 9.89 102.0 12R 5 1530 236.6-246.2 9.6 0.06 0.6 61 R II 1110 709.4-719.1 9.7 4.91 50.6 13R 5 1700 246.2-255.8 9.6 5.34 55.6 62R II 1345 719.1-728.7 9.6 0.13 1.4 14R 5 1845 255.8-265.4 9.6 0.24 2.5 63R 11 2030 728.7-738.4 9.7 9.83 101.0 15R 5 2000 265.4-275.1 9.7 6.66 68.6 64R 11 2300 738.4-747.9 9.5 8.92 93.9 16R 5 2130 275.1-284.8 9.7 1.08 11.1 65 R 12 0200 747.9-757.6 9.7 5.20 53.6 17R 5 2330 284.8-294.4 9.6 2.00 20.8 66R 12 0520 757.6-767.3 9.7 3.84 39.6 18R 6 0100 294.4-304.1 9.7 0.21 2.2 67R 12 0750 767.3-776.9 9.6 8.41 87.6 I9R 6 0230 304.1-313.8 9.7 4.12 42.5 68 R 12 1050 776.9-786.6 9.7 6.19 63.8 20R 6 0410 313.8-323.5 9.7 5.30 54.6 69R 12 1410 786.6-796.2 9.6 2.12 22.1 21R 6 0530 323.5 333.1 9.6 1.07 II.1 22R 6 0940 333.1-342.8 9.7 3.34 34.4 Coring totals 656.2 242.50 37.0 23 R 6 1205 342.8-352.5 9.7 3.17 32.7 Washing totals 140.0 9.54 24R 6 1400 352.5-362.2 9.7 0.01 0.1 Combined totaiIs 796.2 252.04

302 SITE 869

Recovery (%) Logging Run 2: The next logging run was with the FMS tool string. This was lowered in the hole until we discovered that the cable had gone 0 20 40 60 80 100 120 slack and about 680 m of log cable was kinked because the tool string had met an obstruction. The tool string was raised to the surface and about 750 m was cut off the logging cable. The drill string was lowered until the bottom of the BHA was at a depth of 148 mbsf, and the FMS tool string was then lowered until it became blocked at about 166 mbsf. The tool string was raised again to the rig floor, and the drill pipe lowered until the bottom of the BHA was at a depth of about 235 mbsf, about 28 m below the contact between the Cenozoic cherty pelagic sediments and the underlying Upper Cretaceous volcaniclastic sediments, where the caliper log from the first logging run suggested that less rugose hole conditions might prevail. Finally, the FMS tool string passed down the hole to a depth of 774 mbsf and a successful log was made, up to 235 mbsf. The tool string was back on deck at 0930 UTC, 14 May. Logging Run 3 was with the Japanese magnetometer, which was successfully run, beginning at 1000 UTC, 14 May, from a depth of 724 mbsf up to the bottom of the BHA (235 mbsf). This tool was back on deck at 1630 UTC. During a logging run with the geochemical tool string, which obtained successful logs from a depth of 560 up to 360 mbsf, the tool string had to be raised to the surface because time had expired for scheduled downhole operations at Site 869. This run began at Figure 2. Core recovery rates at Site 869 plotted vs. core depth. The dashed 1730 UTC, and the tool was back on deck at 2300 UTC, 14 May 1992. line shows rates for each core, and the solid line represents a 10-point mov- A summary of well-log data from Hole 869B is given in Table 2. ing average. After completion of logging operations, the drill string was re- trieved, the thrusters raised, the acoustic beacon recovered, and the ship made ready for departure. The vessel was under way for Anewetak cut Core 143-869A-18X, the bit advanced only 1 m in 1 hr and the Atoll, the locale of Site 870, at 0830 UTC, 15 May 1992. core barrel returned empty. We concluded that the rocks were too hard for the XCB system and began to pull the drill pipe out of Hole 869A to change bits. The bit was on deck at 1030 UTC, 4 May, ending SITE GEOPHYSICS operations at Hole 869A. Site 869 (proposed Site Syl-3), at H°00.09'N, 164°45.02'E, is Coring Operations in Hole 869B situated on deep seafloor approximately 45 nmi (83 km) southwest of the guyot-atoll pair, Wodejebato and Pikinni (Fig. 5). Its location Hole 869B was spudded in at 2045 UTC, 4 May 1992, at the same was chosen to core redeposited sediments shed by the volcanic depth and about 30 m east of Hole 869A. The rotary bit was washed edifices and their carbonate caps, thus providing data complementary down to a depth of 140 mbsf with a core barrel latched in place to those acquired by Leg 144 drilling on the summit of Wodejebato (Core 143-869B-1W). Normal rotary coring then began in cherty and by prior drilling on Pikinni (Cole, 1954; Emery et al., 1954). Eocene, Paleocene, and Campanian/Maastrichtian strata, from which Wodejebato Guyot has received scrutiny by numerous oceano- core recovery was poor, averaging only about 4% (Table 1). Beginning graphic expeditions, beginning in the 1950s (Emery et al., 1954; at about 217.2 mbsf (Core 143-869B-10R), the lithology changed to Hamilton and Rex, 1959). Recent surveys and dredging were con- graded layers of volcaniclastic sandstone and claystone interbedded ducted on DSDP and ODP site-survey cruises in 1981 (Cruise with marly pelagic limestone, and recovery rates began to improve KK81062604; Peterson etal., 1986) 1988, and 1990 (Cruises MW8 805 markedly (Fig. 2). Coring rates gradually, but irregularly, decreased and MW9009; Lincoln et al., in press) by the University of Hawaii. through the turbidites and debris flows of the Campanian-Turonian, Data collected to date indicate that Wodejebato has had at least two and slowed still further in the highest 100 m of the upper Cenomanian, stages each of volcanism and carbonate-platform formation. The vol- in coarse volcaniclastic debris flows. Below these coarse debris flows, canic pedestal formed prior to the end of the Albian and was topped by coring rates again improved, but then increased gradually toward the an Albian carbonate platform, drowned, was uplifted by a volcanic total depth of Hole 869B at 796.2 mbsf (Figs. 3 and 4). The final core episode during the Santonian, and was again capped by carbonates of (Core 143-869B-69R) was retrieved at 1410 UTC, 12 May, and Campanian to Maastrichtian age (Lincoln et al., in press). preparations begun for logging Hole 869B. In contrast to nearby Wodejebato and Pikinni, the geology and geophysics of the adjacent basin to the west is not as well known, Logging Operations at Site 869 owing to sparse geophysical track-line coverage. Site 869 is located in the Jurassic Quiet Zone about 150 nmi (278 km) north of M29 Following conditioning of Hole 869B, the bit was dropped and the (Nakanishi et al., 1992); thus, the age of the oceanic lithosphere can pipe raised until the bottom of the BHA was at a depth of 90 mbsf. be estimated only by extrapolation. Using the Kent and Gradstein The heave compensator was used during all logging runs; it was (1985) geomagnetic polarity-reversal time scale, the age of the litho- turned on at 177 mbsf for the first logging run and at 344 mbsf for all sphere at Site 869 is approximately 165 Ma. An unknown thickness subsequent runs. of sediment rests upon this oceanic . Perhaps the best analog to Logging Run 1: Beginning at 0100 UTC, 13 May, a string of Site 869 is Site 462, located 195 nmi (361 km) to the south in the logging tools comprising (in order from top to bottom) the gamma- Nauru Basin. At this site, approximately 440 m of Tertiary sediments, ray, sonic, neutron-porosity, density, resistivity, and the Lamont tem- ranging from Paleocene to in age, overlies a Cretaceous perature tools and measuring about 32 m in length, was assembled, section consisting mainly of volcaniclastics and intruded by a Creta- and at 0300 UTC, the string was lowered into the hole to a depth of ceous sill complex (Larson and Schlanger, 1981). An important 778 mbsf. During the upward run, a highly useful set of logs was component in the sediments was redeposited and plant fragments obtained; the tools were back on deck at 0930 UTC. from nearby seamounts showing that islands and carbonate platforms

303 SITE 869

Cutting time (min) Elapsed time (days) 0 50 100 150 200 250 0 1 2 3 4 5 6 7 1 100 - i • 1 1 1 1 1 1 140

380 ——--^^^^

420 t h (mbsf ) 460

Uep i - 500 - 540 - 580 - ————- : 620 - _^_^ : 660 - 700 - 740 - 780 - i . i . i . i

Figure 3. Cutting time for cores in Hole 869B, plotted vs. core depth. Figure 4. Elapsed time for coring operations at Hole 869B plotted vs. depth. The plot begins at spud-in and ends with retrieval of the final core. existed in the region during the Early Cretaceous (Larson and Schlanger, 1981). Similar results were expected at Site 869. Pre-drilling Survey, JOIDES Resolution Site Survey Data (Cruises MW8805 and TUNE08WT) Transiting through the Marshall Islands en route to Site 869, the JOIDES Resolution crossed Wodejebato Guyot from northeast to Proposed Site Syl-3 was chosen along one of the MW88O5 site- southwest so that a 3.5-kHz echo-sounder and 200-in.3 water-gun survey lines trending approximately perpendicular to the trend of the seismic reflection profile could be obtained over its summit (Fig. 7; Pikinni-Wodejebato edifice (Fig. 5). The 80-in.3 water-gun reflection see also "Underway Geophysics" chapter, this volume). record shows (1) the seafloor at a two-way traveltime (twtt) of 6.47 s After leaving Wodejebato Guyot, the ship resumed its cruising and (2) a series of reflectors that gradually fade with depth. These speed of 10.5 kt until reaching a point about 10 nmi (19 km) north of reflectors dip slightly (about 0.3°) away from the volcanic edifices, the proposed site. The ship slowed to 6.5 kt to acquire a good-quality implying that the sediments at this location are from the archipelagic seismic reflection profile over the site with the 200-in.3 water gun. At apron of the atoll-guyot pair. A faint, discontinuous reflector at 0.85 s the same time, an expendable sonobuoy was launched to obtain twtt beneath the seafloor at the site was selected as the deepest visible wide-angle seismic refraction data (see "Underway Geophysics" horizon. Several seismic reflectors just above this horizon appear to chapter, this volume). The first buoy failed part-way along the line, onlap it, thus, the reflector was tentatively identified as a "basement" so another was launched, and the seismic profile was extended 6 nmi of basalt or volcaniclastics. (11 km) past the proposed site (Fig. 8). Another geophysical line across the site, nearly parallel to the Because of the larger seismic source used, the JOIDES Resolution edifice pair, was obtained in January 1992 during cruise TUNE08WT seismic profile has an appearance that is slightly different from the of the Thomas Washington. A seismic reflection record of excellent 80-in.3 profiles obtained during the site surveys. The reflectors near the quality was obtained with an 80-in.3 water gun (Fig. 6). The record surface are not as prominent as in the site-survey profiles, but three shows a series of reflector packets, each of which contains multiple packets of deeper reflectors stand out at 0.20,0.35,0.54, and 0.83 s twtt reflections, interlayered with intervals containing few or weak reflec- beneath the seafloor (Fig. 9). The latter reflector is apparently the one tors (see "Seismic Stratigraphy" section, this chapter). In the middle, identified as "basement" in the site survey lines; however, additional at 0.35 to 0.43 s twtt below the seafloor, is a prominent, continuous, reflections can be seen up to about 1.05 s twtt subseafloor. Assuming and relatively flat series of reflectors that prior to drilling were thought typical deep-ocean-sediment seismic velocities, this observation implies to be Eocene to Late Cretaceous cherts, in analogy with similar layers that the top of the oceanic crust is more than 1 km in depth at Site 869. at the same depth at Site 462. The deepest coherent reflector was Another notable feature of the site-survey and pre-drilling seismic traced at about 0.85 to 0.90 s twtt below the seafloor, corresponding profiles over Site 869 is the roughness of the seafloor and seismic to the "basement" reflector in the MW8805 profile. Extrapolating the reflectors. Unlike most deep-sea sediment layers, which appear nearly velocity-depth profile from Site 462, the depth of this horizon was horizontal in seismic reflection profiles, considerable relief is seen in estimated as approximately 900 mbsf. the layers in the vicinity of Site 869 (Figs. 6 and 9). This relief is SITE 869

Table 2. Well-log data from Hole 869B. 12°30'N

Depth" Log type (mbsf)

Resistivity 89.5-777.2 Bulk density 89.5-774.5 12°00' Neutron porosity 89.5-773.0 Sonic velocity 89.5-772.5 Gamma ray 0-771.3 U-Th-K 360.0-555.8 Aluminum 360.0-558.0 Geochemistry 360.0-560.2 Caliper 89.5-774.5 Formation microscanner 234.8-774.9 cLamont temperature 0-778.5

a Assumes seafloor at 4837.8 m, with all logs correlated and depth shifted to the gamma-ray log from the geophysical tool string. 1 b This log was recorded in drill pipe from 89.5 to 0 mbsf. iroo c This log was recorded in drill pipe from 89.5 to 0 mbsf during the first run, and from 235.0 to 0 mbsf during the runs with the FMS and geochemical tool strings. typically a few hundredths of seconds (twtt), but in places, variability 10°30' of 0.05 s can be noted over a few miles of horizontal distance. Most 164°00'E 164°30' 165°00' 165°30' 166°00' seismic horizons in the area also are laterally discontinuous, with only a few displaying continuity across the entire profile (Fig. 6). Further- Figure 5. Location map for Site 869. Bathymetric contours (in hundreds of more, in places, the reflectors have been interrupted and only dif- meters) at 1000-m intervals are shown as dark lines; auxiliary 500-m contours fracted energy can be seen, suggesting filled channels within the shown in gray. Site-survey ships' tracks across the site, from Cruises MW8805 sedimentary sequence. The 3.5-kHz profile indicates that the seafloor and TUNE08WT, are shown as thin lines, as is track of the JOIDES Resolution. is rough, with hyperbolas, discontinuous reflectors, and depth vari- Solid lines denote portions of seismic lines shown in Figures 6 (A-A'), ations of as much as about 10 m over short distances (Fig. 10). 7 (B-B'), and 9 (C-C) Taken together, these observations imply that sedimentation in the area of Site 869 has been energetic with and patchy Colors vary from pale brown to yellow-brown to dark reddish brown, sedimentation. This agrees with the scenarios that sedimentation and compositions range from nannofossil ooze through radiolarian occurs at this location primarily through turbidity currents and that nannofossil ooze to clayey nannofossil ooze. Thicknesses of the thermohaline bottom currents were strong at times during the Neo- different lithologies are on the scale of tens of centimeters, although gene. The structure of the seismic layering suggests that sedimenta- some bands are thinner. Subunit IA is separated from Subunit IB by tion occurs in archipelagic fan lobes with channels that frequently a strati graphic gap. shift locations. Furthermore, the relief of the seafloor and disconti- nuities imply seafloor erosion, perhaps caused by turbidites or rapid bottom-water currents. Subunit IA Core 143-869A- 1H to Interval 143-869A-4H-3, 79 cm LITHOSTRATIGRAPHY Depth: 0-32.5 mbsf Age: early Miocene Lithologic units have been defined by characteristics such as color, carbonate and clay content, fossil and particle constituents, lithifica- A striking feature of the upper three cores is the presence of tion, sedimentary structures, stratigraphy, and log signature. The nonhorizontal contacts between different lithologies, locally attaining sequence was divided into three major lithologic units: (1) cyclically slopes of 30°. Core 143-869A-1H is dominated by clays containing bedded very pale brown to yellow-brown to dark reddish-brown variable amounts of nannofossils and radiolarians; Cores 143-869A- nannofossil ooze, radiolarian nannofossil ooze, and clayey nannofos- 2H and -3H and Sections 143-869A-4H-1 and -2 by radiolarian- sil ooze; (2) cyclically bedded white to very pale brown to dark nannofossil ooze and nannofossil-radiolarian ooze. These cores are yellowish-brown clayey nannofossil ooze to nannofossil radiolarian heavily bioturbated. ooze to radiolarian ooze containing porcellanite and chert; (3) a series of gray to green breccias and similarly colored, typically graded and parallel-laminated volcaniclastic sandstones interbedded with cal- Subunit IB careous claystones. Intervals 143-869A-4H-3, 79 cm, to -10X-2, 97 cm Depth: 32.5-88.20 mbsf Lithologic Units Age: late Oligocene to late Eocene Unit I In Interval 143-869A-4H-3, 79-82 cm, can be seen a white sand- Core 143-869A-1H to Section 143-869A- 10X-2, 97 cm grade layer, intercalated between brown clayey nannofossil ooze, that Depth: 0-88.20 mbsf contains a mixture of planktonic and large and small benthic foramin- Age: early Miocene to late Eocene ifers, spines and plates, , bryozoans, rare ostra- cods and bivalves, and nannofossils with phosphate and glauconite (see The dominant sedimentary theme of Unit I (Fig. 11) is one of "Biostratigraphy" section, this chapter). The age of the fossil assem- cycles, on various scales, which are characterized by regular changes blage within the redeposited material is earliest Oligocene, which in color and composition (Fig. 12). The principal sedimentary com- makes it older than the upper Oligocene sediment immediately below. ponents are nannofossils, radiolarians, sponge spicules, and clay. The top of this layer, which corresponds to a stratigraphic gap between

305 SITE 869

NW Site 869 SE A'

6.2 o O O o CO o O co o C\J CM CM CM CM CM

6.7

7.2

VE = 47 J | | | | L_ Thomas Washington 29 January 1992 Course 133

Figure 6. Seismic reflection profile across Site 869, shot with an 80-in.3 water-gun source. Time is shown on the horizontal axis; two-way traveltime on the vertical axis. Data were acquired by the Thomas Washington of Scripps Institution of Oceanography during Cruise TUNE08WT. Location shown in Figure 5.

the uppermost Oligocene and lowermost Miocene, is taken to define burrow systems are superimposed upon and interpenetrate one an- the boundary between the two subunits. other. Very similar tiering of trace-fossil assemblages has been de- Nannofossil ooze is the dominant lithology throughout Section scribed from modern deep-sea environments by Wetzel (1991). This 143-869A-4H-3 to Core 143-869A-9H. The discordant bedding that section also contains several millimeter- to centimeter-thick levels of is so characteristic of the upper three cores is also manifest in Sections graded radiolarian sand that exhibit sharp contacts with the envelop- 143-869A-5H-3, -7H-2, and -6H-6 and is particularly striking in ing clayey radiolarian ooze. Radiolarian ooze, colored in various Section 143-869A-8H-2, where sedimentary dips reach 90° and the shades of yellowish-brown, becomes a progressively more important strata show appreciable soft-sediment deformation. sediment type in Cores 143-869A-12X through -15X, where it con- tains subsidiary and variable amounts of clay and nannofossils. Those Unit II levels containing abundant nannofossils in Core 143-869A-15X are chalky in texture. In Cores 143-869A-16X and -17X, only very dark Interval 143-869A- 10X-2, 97 cm, to Core 143-869A-18X gray or brown chert, showing conchoidal fracture and vitreous luster, Depth: 88.2-166.5 mbsf was recovered. Age: late Eocene to middle Eocene Unit HI Core 143-869B-2R to Interval 143-869B-9R-1, 10 cm Depth: 140.0-207.7 mbsf Interval 143-869B-9R-1, 10 cm, to Core 143-869B-69R Age: early Eocene to late Campanian-early Maastrichtian Depth: 207.7-796.2 mbsf Age: early Maastrichtian/late Campanian to late-middle Cenomanian As in Unit I, the dominant sedimentary theme of Unit II is one of cycles on various scales characterized by regular changes in color and Unit III is characterized by the presence of repeated sequences of composition. In Core 143-869A-10X, the first porcellanite appears; gray to green volcaniclastic sandstones and breccias intercalated this is associated with clayey nannofossil ooze. Porcellanites and between lighter-colored nannofossil and radiolarian claystones. In cherts appear intermittently at first, but increase in percentage down- Subunit IIIA, the intercalated claystones are generally grayish-green hole until they constitute the dominant recovered lithology. Also and zeolitic; in Subunit IIIB, they are grayish brown to dark reddish included in this section are Cores 143-869B-2R to -9R, whose recov- brown, radiolarian-rich and the redeposited component is less signifi- ered lithology is dominated by porcellanite and chert, colored various cant; in Subunit IIIC, sedimentary colors return to greenish gray and shades of brown, locally containing radiolarians, and accompanied in olive gray. Subunit HID is characterized by thick (meter-scale) beds some places by nannofossil limestone. of green volcaniclastic breccia containing clasts of basalt interbedded Well-preserved trace fossils are a feature of Section 143-869A- with thinner (tens of centimeters-scale) volcaniclastic sandstone. 12X-2: recognizable forms include Chondrites, Planolites, Teichich- Subunit HIE is characterized by the presence of volcaniclastic sand- nus, and Zoophycos (Figs. 13 and 14; cf. Warme et al., 1973), and the stones and interbedded reddish radiolarian clay stone and nannofossil SITE 869

NE SW B'

1.4

1.8

2.2

2.6

3.0

3.4

3.8

4.2 5 km

JOIDES Resolution 2 May 1992 Course 195° Figure 7. Seismic reflection profile over Wodejebato Guyot, shot with a 200-in.3 water gun. Time is shown on the horizontal axis; two-way traveltime on the vertical axis. Data were acquired by the JOIDES Resolution on approach to Site 869. Location shown in Figure 5. chalk with minor intervals of breccia. Subunit HIE is separated from present. This bivalve is a not uncommon constituent of Upper Creta- Subunit IIIF at the contact by one such level of breccia with an ceous deep-sea drilling cores from all major ocean basins. The clay- underlying volcaniclastic siltstone. Subunit IIIF essentially consists stones are locally burrowed, and in Section 143-869B-20R-1, contain of dark greenish gray volcaniclastic sandstones to siltstones, varying burrows attributed to Planolites and vertical traces similar to Skolithos; in structure from massive to graded and parallel laminated, and in other levels, they reveal a faint millimeter lamination. Claystones in interbedded with calcareous claystones. Subunit IIIG contains thin- Cores 143-869B- 10R through - 19R are more calcareous than those in bedded volcaniclastic sandstone, siltstone and claystone interbed- Cores 143-869A-20R to -26R. ded with nannofossil limestone and radiolarian siltstone. The base The volcaniclastic sandstones are typically colored gray through of this subunit was not reached. A summary of the lithology is given dark gray through greenish-black to black. Typically, they have a sharp in Figure 15. base, are locally scoured and graded and show a variety of sedimentary structures, such as massive units, pervasive parallel lamination and Subunit MA minor cross-lamination (Fig. 16). Most of the grains are sand grade; some basal units extend up to granule size. The organization and Interval 143-869B-9R-1, 10 cm, to Core 143-869B-26R bedding patterns of these redeposited units are illustrated and discussed Depth: 207.7-381.5 mbsf in more detail below. Age: early Maastrichtian/late Campanian to early Campanian In terms of composition the basaltic parentage of the grains is obvious: they comprise zeolites, clinopyroxene, opaque oxides, palag- Subunit IIIA comprises a series of volcaniclastic sediments inter- onite, feldspars, epidote, chlorite, and opaques. A significant feature calated between claystones of brownish gray to light brown color is the presence of associated shallow-water material in the cores of (typical of Cores 143-869B-10R to -19R) and gray to greenish gray this subunit, typically being concentrated in the coarser basal layers color (typical of Cores 143-869B-20R to -26R) that are variably rich of the graded units. Such material is particularly noticeable in Sections in nannofossils. In one particularly calcareous level in Interval 143- 143-869B-11R-1 and -2, of early Maastrichtian-late Campanian age, 869B-11R-3, 22-24 cm, a well-preserved specimen of Inoceramus is where it includes bivalve, echinoid, and red-algal fragments, "orbitoid

307 SITE 869

I 1

"Ic 1400- 2 May 92

CΛJ C\J en δ• tIT,] in 1500 o s o §88 o - o CD ° ^ ° 0000 03 May 92 _ " L. o o 1 Site 869

1600-I 1700-L c

10°50' -

| 164°30'E 164°40' 164°50' 165°00'

Figure 8. JOIDES Resolution track chart for the vicinity of Site 869. C-C 7.4 denotes the ends of seismic reflection profile in Figure 9.

foraminifers," "micritic ooids," and glauconite. Other specific exam- 7.8 ples include Interval 143-869B-22R-3, 26-27 cm, which contains JOIDES Resolution 2 May 1992 Course 187C

much recrystallized skeletal and angular fragments of pelletal 3 grainstone, and Interval 143-869B-25R-1, 40-50 cm, the basal frac- Figure 9. Seismic reflection profile over Site 869, shot with a 200-in. water tion of a graded layer of early Campanian age, which yields benthic gun. Time is shown on the horizontal axis; two-way traveltime on the vertical foraminifers, possible recrystallized red algae, bivalve fragments, and axis. Data were acquired by the JOIDES Resolution on approach to Site 869. concentrically laminated micritic ooids. Scattered benthic foramini- Location shown in Figures 5 and 8. fers and fragments of macrofossil skeletal calcite also occur within more finer-grained volcaniclastic siltstones, as in Interval 143-869B- Subunit IIIC is essentially similar to Subunit IIIA in that it consists 26R-1, 34-36 cm. of graded gray to greenish-gray volcaniclastic sandstones to siltstones interbedded with finer-grained calcareous levels, zeolitic (clinoptilo- Subunit II IB lite), and locally contains radiolarians. Some chert and minor silicified claystone is seen. Grain-types recognized include feldspar, clinopyrox- Cores l43-869B-27Rto-34R ene, chlorite, opaques, and zeolites. Shallow-water grains accompany Depth: 381.5-458.8 mbsf these igneous components in some of the graded beds: in Interval Age: early Campanian to middle/late Turonian 143-869B-34R-1, 142-144 cm, a wealth of bioclastic detritus with micritic ooids was observed; Interval 143-869B-35R-1, 44^1-6 cm, This subunit is dominantly composed of radiolarian claystone to contains abundant micritic ooids and large benthic foraminifers; Sec- siltstone, grayish-brown to dark reddish-brown in color, locally cal- tion 143-869B-36R-1 yielded large foraminifers (orbitolinids), echi- careous and zeolitic. The dominant zeolite is clinoptilolite, according noids, gastropods, and ooids. An interesting feature of this subunit can to shipboard XRD data. Redeposited volcaniclastic material occurs be observed in the gamma-ray log, namely a positive excursion at the only in millimeter-thick laminae in Cores 143-869B-27R through level of Core 143-869B-37R, close to the Cenomanian/Turonian -30R. In Cores 143-869B-31R through -33R and the upper part of boundary. On the other hand, the geochemical log shows that this Core 143-869B-34R, the graded greenish-black volcaniclastic sand- interval has been enriched in potassium, but not in uranium. This stones characteristic of Subunit IIIA have been intercalated between suggests ashy, rather than organic-rich, beds. the radiolarian-rich strata. Convolute bedding can be seen in Interval 143-869B-34R-1, 132-135 cm, in the upper part of a graded volcani- Subunit HID clastic layer (Fig. 17). Radiolarian concentration is variable; the microfossils may be distributed throughout the groundmass or con- Interval 143-869B-38R-1, 6 cm, to Section 143-869B-42R-CC centrated in millimeter-scale beds. Laminations occur in this pelagic Depth: 487.8-536.1 mbsf facies where it has been intercalated between redeposited beds; Age: late Cenomanian elsewhere, it may be bioturbated. Shallow-water material, such as micritic ooids and peloids, is present in the redeposited units. Chert Subunit HID is characterized by the presence of green volcani- occurs in radiolarian siltstone in Core 143-869B-30R. The contact clastic breccias, the clasts of which may be rodlike to equant in with the underlying subunit is gradational. shape, angular to subrounded, and range in size up to 80 mm. Most of the large clasts are subrounded (e.g., clasts in Intervals 143-869B- Subunit IIIC 41R-4, 69-76 cm, and -42R-2, 87-92 cm), and the elongated frag- ments tend to be horizontal in orientation. Another interesting feature Core 143-869B-35R to Interval 143-869B-38R-1, 6 cm of these clasts is that their lower side is characteristically rimmed Depth: 458.8^87.8 mbsf (-0.1-1 mm) with white zeolite. Zeolites also fill a few thin (0.1- Age: middle/late Turonian to late Cenomanian 2 mm) fractures that cut the volcaniclastic breccia in some places

308 SITE 869

7.0 JOIDES Resolution 2 May 1992 Course 187C Figure 10. 3.5-kHz echo-sounder profile over Site 869. Time is shown on the horizontal axis; two-way traveltime on the vertical axis. Data were acquired by the JOIDES Resolution on approach to Site 869. Location shown in Figures 5 and 8.

(Fig. 18). The dominant zeolite-group mineral (identified by XRD) is more altered and more angular than the large clasts. They are ran- analcite, which is accompanied locally by trace quantities of phillip- domly distributed throughout the matrix, although a few pockets seem site and thomsonite. to have more glass shards than others. The clasts are generally polymictic, although almost all the large (>l cm) ones are basaltic. The dominant type is bluish-gray, aphyric SubunitIHE to sparsely phyric, slightly to moderately altered or plagio- clase-pyroxene- basalt. Generally, the phenocrysts are no more Core 143-869B-43R to Interval 143-869B-55R-2, 26 cm than 2 mm in size and are set in a groundmass of quenched plagio- Depth: 536.1-653.3 mbsf clase, dust of opaque oxides, and interstitial glass, with the latter Age: middle to late Cenomanian altered to calcite and clay minerals, including chlorite. Plagioclase phenocrysts occur as anhedral to subhedral stubby laths that range Subunit HIE comprises dark green volcaniclastic sandstone with from fresh to moderately altered; pyroxene phenocrysts are anhedral interbedded reddish-brown radiolarian claystone, locally silicified, and to subhedral grains that are slightly to moderately altered. Olivine clayey nannofossil chalk. The claystones are generally laminated but occurs as anhedral to euhedral prisms that are completely pseudo- bioturbated levels do occur. The sandstones consist of altered glass and morphed by clays with minor calcite; a trace of (

MY) SITE 869

0 Other breccias are finer-grained, being dominantly composed of layey nannofossil ooze granule- to fine pebble-sized clasts. lower Miocene Subunit IIIF IA Intervals 143-869B-55R-2, 26 cm, to -68R-3, 79 cm 20- Radiolarian nannofossil ooze Depth: 653.3-780.7 mbsf Age: middle to late Cenomanian Turbidite with benthic 32.5 foraminifers, echinoids, Subunit IIIF is composed primarily of dark greenish-gray to green- upper red algae, bryozoans, ish black volcaniclastic sandstones and siltstones with scattered dis- Oligocene glauconite, phosphate, 40- Unit crete levels of lighter-colored nannofossil-rich siltstone to limestone and carbonate grains and some radiolarian-rich layers. The igneous grains are largely con- stituted by yellowish volcanic glass, variably palagonitized with pro- Nannofossil ooze nounced brown rims where alteration has been maximized, together lower with fresh clinopyroxene, aphyric to moderately phyric basaltic clasts, and rare plagioclase. The glasses range from aphyric to vitriphyric with Oligocene IB 60- subhedral to euhedral, slightly altered clinopyroxene as the dominant phenocrystic phase; alteration to smectite is commonplace. A wide range of sedimentary structures, such as grading, wavy, cross- and parallel-lamination is present, but significant intervals of both the sandstones and siltstones are essentially structureless. In Clayey nannofossil ooze 80- terms of thickness, the strati graphically lowest beds are only a few centimeters thick, whereas the higher graded units are typically on a Q_ CD scale of meters or a little less, and some of them have erosional bases. Q 88.2 A number of divisions of the Bouma Sequence are clearly identifiable •xfcrax throughout the subunit; and a sole mark is recognizable in Interval upper 143-869B-64R-3, 86 cm. Soft-sediment deformation is present in 100- Eocene Interval 143-869B-63R-3, 17-34 cm. Evidence for bioturbation, in- Nannofossil ooze with chert cluding escape burrows, can be found, but is uncommon. Radiolarians occur intermittently throughout the subunit (locally filled by zeolites or green smectite), but also are concentrated in interturbidite siltstones, commonly as millimeter-thick layers, as for example in Intervals 143-869B-67R-1,91 cm; -67R-5,91 cm; -67R-5, 120- L JL J 99 cm; and -67R-6, 61 cm. Unit II US1*1 middle Subunit IIIG Eocene Nannofossil radiolarian ooze with chert Interval 143-869B-68R-3, 80 cm, to Core 143-869B-69R Depth: 780.7-796.2 mbsf 140- Age: middle-late Cenomanian m ts. This subunit mainly consists of greenish-gray, fine-grained vol- caniclastic sandstones and siltstones showing parallel-and cross-lami- nation and alternating with zeolitic claystones on a scale of tens of 160— centimeters. Interval 143-869B-68R-4, 25-76 cm, contains faintly 166.5 laminated, light greenish-gray clayey nannofossil limestone, brown- ish-gray claystone, and chert. The interval has been disturbed by Rock and sediment type drilling, so that the interrelation of these lithologies could not be established. Interval 143-869B-68R-5, 58-67 cm, is radiolarian-rich Nannofossil radiolarian Clayey nannofossil ooze ooze limestone displaying millimeter-thick parallel laminations (Fig. 22). Oblique bedding, soft-sediment deformation, and locally brecciated Chert and porcellanite Nannofossil ooze siltstone layers are common in Sections 143-869B-68R-4 and -5. The base of this subunit was not reached. Radiolarian nannofossil ooze Interpretation of Sedimentary Environments Figure 11. Stratigraphic column for Hole 869A. Deposition of Unit III began, in mid- to late Cenomanian time, are a number of intercalations of volcanic breccia, the most important with deposition of dark-colored volcaniclastic sandstones to siltstones of which is a thick dark greenish gray to greenish black level that set against a background pelagic sedimentation of nannofossils and occurs from Section 143-869B-54R-1 to Interval 143-869B-55R-2at radiolarians (Subunits IIIF and IIIG). The sedimentary structures in 26 cm, and the base of which is taken to define the lower boundary the volcaniclastics indicate deposition by turbidity currents. No evi- of the subunit. The clasts in this unit are subrounded to subangular, dence was found of any contribution of shallow-water material to the graded, and of centimeter scale; locally, they carry zeolite rims and sediment, which is in contrast to the situation higher in the sequence. in some places, the precipitate becomes a major pore-filling cement Subunit HIE was characterized by the deposition of volcaniclastic (Fig. 21). The zeolites have been identified as analcite and chabazite sandstones and breccias, which interrupted the background sedimen- by XRD. The fabric of the rock varies from clast- to matrix-supported. tation of clay, radiolarians, and nannofossil ooze. Repeated influxes

310 SITE 869

cm cm 55

10- 57-

12-

59-

14-

61 -

16-

63- 18-

20^ 65-

22 -1 67-

24- 69-

26-

71 -

28-

73- 30-

75-1 32-1 Figure 13. Mixing of lighter radiolarian-nannofossil and darker nannofossil- Figure 12. Centimeter-scale color banding caused by varying ratios of nanno- radiolarian oozes resulting from intense bioturbation. Recognizable trace fossils fossils vs. radiolarians. Radiolarian-rich ooze is darker. Note inclination of include Teichichnus (T), Zoophycos (Z), Planolites (P), and Chondrites (C). layers toward the right of photograph (Interval 143-869A-3H-6, 8-32 cm; age, Some synsedimentary soft-sediment deformation occurs locally (SD). A sharp early Miocene). contact (arrows) between muddy sediment below and sandy sediment above indicates the base of a graded radiolarian layer (Interval 143-869A-12X-2, 55-75 cm; age, late Eocene).

311 SITE 869

cm of turbidity currents carried basaltic sand to the site. Large clasts were probably transported by debris flows, but the absence of a clay matrix in many deposits suggests frequent transport by grain flow. The inclined sedimentary contacts in Cores 143-869B-50R and -52R 104- suggest soft-sediment deformation on a sloping seafloor. Some shal- low-water material, such as orbitolinid foraminifers, derived ooids, or oolitic limestone and, more specifically, the coalified woody frag- ments, indicate the presence of one or several emergent volcanic islands that acted as a sediment source. Subsequently, during late Cenomanian time, came the deposition 106- of coarse, poorly sorted basaltic breccias comprising multiple units of amalgamated graded beds (Subunit HID). Deposition as debris and grain flows is suggested by these and other sedimentary features, such as locally observed inverse grading. Most of the large clasts were probably derived from nearby that were erupted/intruded at considerable water depth because these are generally fine-grained and 108— aphyric. Sheet flows or thin intrusive sills or dikes, which gen- erally cool rapidly, are the most likely source. Certainly the domi- nance of abundant glass shards implies that some of the basalt was erupted underwater. The phenocryst assemblage suggests that these are most probably only mildly alkalic or intraplate tholeiitic in com- position and are not highly alkalic. The smaller clasts, deriving 110- perhaps from more distant regions, are more varied in texture and composition, and the presence of free-floating pyroxene crystals suggests a source of highly pyroxene-rich megaphyric basalt. The bivalve fragment in Interval 143-869B-54R-3, 26 cm, and the very sparse carbonate grains in Section 143-869B-45R-4, including a recognizable echinoderm fragment, could suggest, albeit equivocally, 112- that distal modest-depth environments may have existed in the region. Generally, however, such material was not supplied or was over- whelmingly diluted by volcaniclastic detritus. The subrounded form of the basaltic clasts indicates transport paths of considerable distance. Diagenesis of this material involved devitrification of glass shards and their replacement by zeolite as well 114- as precipitation of zeolitic cement in available pore space; shelter pores under the larger clasts were an important site for such cement. A change in the pattern of sedimentation followed, with the depo- sition of Subunit IIIC occurring around the time marked by the Cenomanian/Turonian boundary. Coarse centimeter-scale debris was no longer deposited at the site, and the pattern of sedimentation 116- switched to that typical of turbidites with the emplacement of sand- and silt-grade material (Fig. 15). This change from proximal to distal facies can be interpreted in terms of the Cenomanian-Turonian rise in sea level commonly viewed as eustatic (e.g., Hancock and Kauffman, 1979; Schlanger, 1986), which partially flooded the source terrain. Alternatively, volcanism may have waned or ceased in the region supplying detritus. Sources for the igneous material presumably lay in 118- shallow water, given the presence of shallow-water carbonate debris in the graded volcaniclastics. The shallow-water material indicates a normal-marine source area and may have derived from an off-bank environment; it is notable, for example, that the ooids are concentri- cally laminated and micritic and resemble the pelagic "ooids" de-

1 scribed from a number of "deeper-water" environments in the Tethyan- 120- Atlantic and Pacific Mesozoic (Jenkyns, 1972; Schlager, 1980; Hag- Figure 14. Large Teichichnus burrow (T) cutting through white nannofossil gerty and Premoli Silva, 1986). Nannofossils, planktonic foraminifers, ooze. A sharp contact (arrows) between darker, muddy sediment below and and radiolarians were being supplied as a background sediment during lighter, sandy sediment above identifies the base of a graded radiolarian this period and were diagenetically altered to produce calcareous interval. Silicified claystone (SC) forms a hard layer. Deformation is caused siltstones and chert. mostly by drilling disturbance, but may also be partly from burrowing and During the deposition of Subunit IIIB, the background sedimen- synsedimentary differential compaction (Interval 143-869A-12X-2, 103- tation consisted of brown and reddish-brown radiolarian claystone 120 cm; age, late Eocene). and siltstone. Initially, the supply of volcaniclastic material was maintained, while later, the influx of material waned or was directed elsewhere, with a consequent increase in the proportion of the pelagic component deposited. However, with the deposition of Subunit IIIA, deposition of sand-grade volcaniclastics recommenced with the de- velopment of typical turbidites.

312 SITE 869

U •l» •fa •A• i Nannofossil ooze b• Jhi -•- •A• i

100- Chert b. ^ i Λ. .

I. Pal.- Radiolarian-nannofossil ooze and nannofossil-radiolarian ooze Unit j\ Λ Λ J• e. Eoc. IV J"L α'fc α'i. Radiolarian ooze 200^ with porcellanites and chert , A A A i -207.7 Volcaniclastic breccia, Volcaniclastic sandstone to siltstone with nannofossil-rich •/s.Ss. /s.•/' sandstone and siltstone 300- claystone intervals interbedded with local calcareous-rich levels Interbedded calcareous claystone with some radiolarians 400- Sant.- Radiolarian claystone to siltstone and volcaniclastic sandstone Zeolitic claystone Q. Tur. Q M9 AsforSubunit IIIA 500- Volcaniclastic breccia 536.1

Volcaniclastic sandstone and breccia interbedded with 600- radiolarian claystone and clayey nannofossil chalk

700- Volcaniclastic sandstone-siltstone with rare nannofossil-rich siltstone and radiolarian-rich layers

796.2 Volcaniclastic siltstone and calcareous claystone with radiolarianε

Figure 15. Stratigraphic column for Hole 869B.

The sedimentary evolution of Unit III can be explained in terms The thick, meter-scale beds of volcaniclastic breccias and sand- of the classical models proposed for siliciclastic submarine fan sys- stones of Subunit HID again indicate a proximal setting, at a canyon tems (e.g., Normark, 1970; Mutti and Ricci Lucchi, 1972; see also outlet or in deep channels on the inner fan, if a point source was Pickering et al., 1989). Figure 23 shows the observed turbidite se- present, or over large distances at the base of the slope, if sediment quences and grain debris-flow deposits in Unit III. Figure 24 is a aprons predominated. The general absence of a muddy matrix and the compilation of features, such as predominance of turbidite intervals, observed shelter pores under large clasts suggest transport by grain according to the Bouma classification, maximum thicknesses of mass flow, whereby the sand-sized grains acted as a transporting agent for flows, maximum organic carbon contents, and influx of shallow- the larger fragments. In coarse material, packing was locally very water carbonate grains. In this figure, we also attempt an interpreta- loose, and pore space was rapidly filled by zeolitic cements (Fig. 21). tion of the depositional environments. A very rapid change from deposition of proximal to distal facies Subunit IIIG displays thin, fine-grained turbidites that are domi- occurred during the late Cenomanian: this is registered as a pro- nated by the Td interval and that also contain Tc-Td couplets. This nounced facies change in the top of Core 143-869B-38R, at the suggests a depositional environment on the outer fan. Local scouring boundary between Subunits IIIC and HID (Fig. 24). The relative and deposition of Ta intervals, as well as soft-sediment deformation abundance of couplets of thin, fine-grained Bouma divisions Tc and and inclined bedding, indicate that at times fan lobes prograded Td suggests deposition on the outer fan, whereas the return to slightly rapidly toward the basin. Nannofossil limestone, radiolarian siltstone, coarser facies in Core 143-869B-35R implies a minor progradation and chert in Core 143-869B-68R represent distal facies that were of the fan system. It is important to note that chert occurs in Cores deposited during a rise in relative sea level, or during a period of 143-869B-37R and -35R, and that in Core 143-869B-35R the tur- volcanic quiescence. bidites have been silicified. The change to Subunit IIIF is very abrupt (Figs. 23 and 24). Thick The lower part of Subunit IIIB contains thin Tc and Td divisions turbidite sequences with well-developed Ta intervals, which fine of volcaniclastic sediment (Fig. 27), which suggests an outer-fan upward into Tc-Td couplets, suggest channel fills on the middle fan. setting. The upper part of this subunit is dominated by pelagic Sediment supply was high and distances of transport fairly long, material, such as red clay and radiolarians, which were found to have which resulted in relatively fine-grained and well-sorted textures. been reworked in a few of the thin turbidites. Volcaniclastic sediment Local levels of larger clasts imply rip-up from channel floors. has been confined to very thin turbiditic layers, suggesting deposition Subunit HIE shows an evolution toward more proximal condi- on the basin plain. tions: grain flows transporting pebble-sized clasts prograded over the Passing up through Core 143-869B-26R, which shows an outer- finer sandstones and siltstones of Subunit IIIF (Fig. 25). Again, fan facies association, the turbidites rapidly become coarser and fining-upward sequences are well developed (Fig. 26), pointing to thicker (Subunit IIIA). Complete Ta-Te turbidites occur commonly channel fills in an inner-fan depositional setting. The top of this (Figs. 16 and 23). This subunit generally exhibits meter-scale se- subunit, however, indicates a shift to more distal conditions (Fig. 24). quences, beginning with densely stacked, fine-grained Tc-Td divi-

313 SITE 869

cm cm 130-

2-

132-

4-

r> 134-

Td 8-

136-

10-

12- 138-

14-

140-

16-

18- 142-

20 -

144

22 -

24- 146-

26-

148-

28-

1 30-1 150-

Figure 16. Complete Ta-Te intervals of turbidite in Subunit IIIA on top of Figure 17. Turbidite in Subunit IIIB, showing well-developed convolute bed- amalgamated Ta and Ta-Tb successions. Note bioturbation in Te and partly in ding (Interval 143-869B-34R-1, 130-150 cm). Td level (Interval 143-869B-23R-2, 0-30 cm).

314 SITE 869

cm cm 70 • 117

72- 119 •

74-

121 "

76 H

123-

78-

125 -1 Figure 19. Water-escape structures (dish structures, arrows) in Tc interval of a turbidite in Subunit HIE (Interval 143-869B-51R-2, 117-125 cm). 80-

observed in Subunit IIIA (Fig. 24) were the result of such autocyclic processes, of sea-level fluctuations, or of variations in sediment sup- ply. The genera] trend, however, was from a more proximal to a more distal middle-fan environment. 82- The early Campanian-early Maastrichtian interval also saw a change in color of the accompanying claystones from the reddish- brown of Subunit IIIB to the greenish-gray of Subunit IIIA, which may reflect the increased volume of fine-grained igneous material therein, as well as indicate more rapid burial rates, preventing seafloor oxidation of iron compounds. Redeposition of shallow-water material 84- from reef-fringed volcanic islands during Campanian-Maastrichtian time is a regional phenomenon across much of the central Pacific Ocean that affect the Line Islands and the Nauru Basin west of the Marshall Islands (Schlanger and Premoli Silva, 1981; Schlanger et al., 1981) and seems to have resulted from a final phase of volcanism Figure 18. Volcaniclastic breccia (grain to debris-flow deposit) with fine, in the area. zeolite-filled fractures showing white on photograph (Interval 143-869B- In many cases, the turbidites in Unit III containing redeposited 54R-2, 70-85 cm). shallow-water material occur in rather distal facies of the middle to outer fan (Fig. 24). This might suggest that either the shallow-water sions, which are abruptly overlain by a fining and thinning-upward material was strongly diluted by rapid volcaniclastic sedimentation turbidite succession. Bioturbated Te divisions become more impor- in a proximal setting, or that transport of carbonate particles from a tant toward the top of these sequences (Fig. 28). Commonly, the shallow ramp or bank was only possible when relative sea level was bioturbation has mixed sediment from the Td and Te divisions high. The contents of total organic matter are generally very low in (Fig. 29). The fine-grained basal part may correspond to overbank Unit III (see "Organic Geochemistry," this chapter). However, higher- deposits, whereas the fining-upward succession can be interpreted as than-average values seem to correlate with relatively distal facies, a channel fill (Mutti and Ricci Lucchi, 1972). These small-scale where sedimentation rates were low (Fig. 24). sequences are stacked in larger sequences, which show a thickening- Supply of volcaniclastic sediments to Site 869 ceased rather and coarsening-upward trend (Figs. 23 and 24). Such a facies asso- abruptly and, at the onset of Unit II time (early Eocene), deposition ciation is characteristic for the middle-fan depositional environment, of radiolarian oozes became dominant. The sedimentary record of the where channelled lobes prograde because sediment was supplied at early Eocene interval is largely represented by diagenetic equivalents fairly rapid rates. Slumps occur locally and suggest the development of these oozes, namely porcellanites and cherts. Mid-Eocene sedi- of inner-fan complexes. Avulsion and channel switching are common ments are dominated by remarkably pure radiolarian oozes. Their in these settings. From the present information, one can not conclude bioturbated intervals indicate periods of good oxygenation of the whether the variations from more proximal to more distal facies bottom waters and relatively high sedimentation rates (Wetzel, 1991).

315 SITE 869

cm cm 43- 48

45- 50-

52- 47^

54- 49-

56- 51 -1

Figure 20. Flattened and slightly imbricated mud clasts in grain to debris-flow deposit of Subunit HIE (Interval 143-869B-52R-4, 43-51 cm).

The overall change upsection from sediment dominated by radio- 58- larians (Unit II) to that increasingly dominated by nannofossils (Unit I) Figure 21. White zeolite cement fills large pores in loosely packed volcaniclas- can be interpreted in terms of changes in fertility of near-surface waters or in the level of the calcite compensation depth (CCD), or a combi- tic breccia. Note shelter effect beneath larger clasts (Interval 143-869B-54R-4, nation of the two. The present-day equatorial Pacific Ocean is a zone 48-58 cm). of relatively high productivity, and radiolarian-rich sediments pre- dominate in depths close to or below the CCD level (Lisitzin, 1971). the strata in the upper cores, which may have been imposed by It is likely that Site 869 lay under the equator during mid- to late Eocene soft-sediment slippage; the vertical strata in Core 143-869A-8H time and received such sediments until northward passage of the suggest the local presence of slump folds. That conditions on the Pacific Plate moved it into less fertile waters dominated by nannofos- seafloor were generally conducive to life is indicated by the abundant sils (e.g., Berger and Winterer, 1974). Alternatively, the facies change traces of bioturbation and the relatively diverse trace-fossil assem- may be viewed simply as a response to an early Oligocene decrease in blages throughout many levels in the cores. the CCD from a mid- to late Eocene high: such changes are docu- mented from a number of Pacific Ocean sites (van Andel, 1975). BIOSTRATIGRAPHY Superimposed on this general trend was a high-frequency variation in the nature of the sediment imposed by changes in the proportionality Calcareous Nannofossils of nannofossils, radiolarians, and clay. Cycles of one type or another are known from virtually all pelagic sediments and are now conven- Hole 869A tionally attributed to orbitally induced climatic variation that controlled Calcareous nannofossil biostratigraphy of Hole 869A indicates a such factors as biogenic productivity, influx of eolian clay, deep-sea lower Miocene sequence unconformably overlying a relatively ex- dissolution of carbonate, either singly or in combination (e.g., Fis- panded Oligocene-Eocene section. Excellent APC/XCB core recov- cher, 1986). ery renders this a sequence of biostratigraphic utility, although nanno- The presence of graded radiolarian oozes in Section 143-869A- fossil preservation is moderate to poor throughout. The following 12X-2 implies local downslope transport by turbidity currents, and summary is based largely on the investigation of core-catcher sam- evidence for redeposition of material from distal shallow-water sites ples, although more detailed toothpick sampling was conducted in is provided by the carbonate sand layer in Interval 143-869A-4H-3, stratigraphically important intervals. 79-82 cm, which contains an array of redeposited shallow-water The uppermost sediments recovered in Hole 869A belong to early material. Although of early Oligocene age, these grains were trans- Miocene age nannofossil Zone NN2 of Martini (1971) (Fig. 30). ported during late Oligocene time, and their emplacement likely re- Samples 143-869A-1H-1, 30 cm, to -4H-3, 78 cm, contain a combina- flects the regional erosional event affecting mid-Pacific atolls (e.g., tion of the following species: Discoaster druggii, Sphenolithus dis- Anewetak), correlative with a decrease in glacio-eustatic sea level similis, Triquetrorhabdulus carinatus, Cyclicargolithus floridanus, (Schlanger and Premoli Silva, 1986). The unconformity within the Discoaster variabilis, Discoaster deflandrei, and Dictyococcites pelagic section (uppermost Oligocene-lowermost Miocene) immedi- scrippsae. Interestingly, Sphenolithus belemnos, which normally oc- ately above the redeposited layer is slightly younger than the ero- curs in this zone, is absent. A thin, white, graded sand recovered sional/solutional gap calibrated from the shallow-water sequence of between Samples 143-869A-4H-3, 79 and 82 cm, contains an Oligo- Anewetak Atoll, and the two phenomena apparently are not related. cene assemblage consisting of Dictyococcites bisectus, Ericsoniafor- Indications of bottom slopes are provided by the considerable dip of mosa, Reticulofenestra umbilica, Sphenolithuspredistentus, and S. ra-

316 SITE 869

cm The Oligocene of Hole 869A has been subdivided as follows: 50 Oligocene Zone NP24 extends from Sample 143-869A-4H-3, 85 cm, to -4H-CC; Cores 143-869A-5H and -6H belong to Oligocene Zone NP23, based on the occurrence of Sphenolithus predistentus and absence of S. ciperoensis and Reticulofenestra umbilica. Oligocene Zone NP21 extends from Sample 143-869A-7H-2, 47 cm, to -9H-4, 20 cm, based on the occurrence of Ericsonia formosa, Ericsonia 52- subdisticha and Reticulofenestra umbilica and the absence of Dis- coaster barbadiensis and Discoaster saipanensis. A detailed analysis was conducted of the transition between Zones NP20 and NP21, often taken to identify the Eocene/Oligocene boundary. This boundary, which can be defined by the last occurrence of D. saipanensis and, alternatively, by the last occurrence of D. barbadiensis, lies between 54- Samples 143-869A-9H-4, 20 cm, and 50 cm. This interval, which corresponds to an interval of brown clayey nannofossil ooze, is marked both by a dramatic decrease in the abundance and scattered occurrence of both boundary markers. Similar problems were experienced in the zonal division of the upper Eocene sequence of Hole 869A, as happened with previous 56- Leg 143 sites. Owing to the absence of the marker species, we had to rely on secondary markers. The interval from Samples 143-869A- 9H-4, 50 cm, to -10X-1, 0 cm, was placed in Zone NP20, based on the occurrences of D. barbadiensis, D. saipanensis, and E. subdis- ticha. Samples 143-869A-11X-3, 113 cm, and -11X-5, 22 cm, prob- ably belong to upper Eocene Zones NP18 and NP19, as suggested by 58- the absence of both E. subdisticha and Chiasmolithus grandis. The interval from Samples 143-869A-11X-CC to -12X-CC contains an assemblage that includes Sphenolithus furcatolithoides, Chiasmo- lithus grandis, Chiasmolithus solitus, and R. umbilica. These occur- rences and the absence of Chiasmolithus gigas indicate that this interval lies in middle Eocene Zones NP16 and NP17. Middle Eocene 60- Zone NP15 extends from Samples 143-869A-13X-5, 15 cm, to -14X-6, 40 cm, based on the occurrence of Sphenolithus furcatolithoides and C. gigas and the absence of R. umbilica. We tentatively assign the lowermost fossiliferous sediments in Hole 869A, in Samples 143- 869 A-14X-CC and -15X-CC to lower and middle Eocene Zones NP 13 and NP14, based on the occurrences of Discoaster lodoensis and 62- Reticulofenestra dictyoda and absence of Sphenolithus editus, Sphe- nolithus conspicuus and species of Toweius.

Hole 869B Hole 869B was washed to a depth of 140 mbsf. Calcareous 64- nannofossil biostratigraphy of the cored interval of Hole 869B indi- cates about 40 m of Eocene to lower Paleocene sediments overlying approximately 600 m of predominantly clastic sediments of Late Cretaceous age. The hole was abandoned in hemipelagic sediments of Cenomanian age at a depth of 796.2 mbsf. In addition to core- catcher samples, numerous additional samples were examined in 66- critical stratigraphic intervals, or where nannofossiliferous horizons alternated with barren intervals. A total of 119 samples were studied. The preservation is moderate in the uppermost cores (Cores 143- 869B-4R to -15R) and deteriorates considerably downward. In gen- eral, the assemblages from the turbidite sequence (Cores 143-869B- Figure 22. Thinly laminated radiolarian siltstones in Subunit IIIG (Interval 15R to- 28R) and those of the volcaniclastic sequence (Cores 143- 143-869B-68R-5, 50-67 cm). 869B-36R to -69R) show poor preservation. Thus, in several inter- vals, preservational factors lower the attainable biostratigraphic reso- dians which belong to Oligocene Zone NP21. Sediments below this lution. In many intervals of the Paleogene and Cretaceous, we have sand layer, for example, in Sample 143-869A-4H-3, 85 cm, contain relied upon secondary marker taxa to date sediments because of the Sphenolithus ciperoensis, Sphenolithus distentus, and 5. predisten- absence of zonal markers. In these places, we have used the ranges tus, the combination of which indicates an assignment to Oligocene compiled for these species by Perch-Nielsen (1985). Zone NP24. Considered in their sedimentological context, these Uppermost Core 143-869B-1W, which covers the interval from 0 biostratigraphic data suggest that the graded layer was redeposited to 140 mbsf, contains radiolarian nannofossil ooze overlying siliceous from the erosion of older sediment upslope during the late Oligo- mudstone. Two samples were examined from Section 143-869B- cene. The absence of Zones NP25 and NN1 suggests a brief interval 1W-7. A sample from the ooze contains S. predistentus and R. dictyoda, of erosion and/or nondeposition during the latest Oligocene and but lacks S. ciperoensis and R. umbilica, and therefore has been earliest Miocene. assigned to Oligocene Zone NP23. A sample from the mudstone

317 SITE 869

n Core 10R Core 11R .Core13R Core 15R Core 16R Core 17R Core 19R Core 21R Core 22R OTZD—l 0 U - 0T 1—i 0

r

• .2

• n

• Q) 100 100 100- U) 100- nun

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Te, pelagic sedimentation Art Ta, massive, graded, very coarse-grained

Td, upper parallel laminae Grain and debris flows

Tb and Tc, wavy and plane parallel laminae Slump

Ta, massive, graded, coarse-grained

Figure 23. Graphic logs of Bouma sequences and intervals of grain flows and debris flows in Unit III.

contains D. bαrbαdiensis, D. sαipαnensis, R. umbilicα, and C. grαndis, pileαtus and Fαsciculithus stonehengi, and the absence of F. tympαni- indicating a probable correlation to middle Eocene Zone NP17. Chert formis, the first occurrence of which marks the base of Zone NP5. fragments recovered in Cores 143-869B-2R and -3R were undatable, Sample 143-869B-7R-1, 20 cm, contains Cruciplαcolithus tennis, however those in Cores 143-869B-4R to -8R possess stringers of Cruciplαcolithusprimus, and Toweiuspertusus and is also tentatively fossiliferous chalk. Assemblages from Samples 143-869B-4R-1, correlated to Zone NP4. The lowermost Paleocene Zones NP1 to NP3 40 cm, to -5R-1, 94 cm, contain Discoαster multirαdiαtus and D. bαr- were not observed. bαdiensis, indicating that this interval belongs to the lower Eocene The interval between the recovered portions of Cores 143-869B-7R Zone NP 10 of Martini (1971) (Fig. 31). This interval also is constrained and -8R is marked by a second major unconformity that includes the by the presence of minute specimens of Zygrhαblithus bijugαtus and Cretaceous/Tertiary boundary. This correlates to the interval between the absence of Fαsciculithus tympαniformis in Sample 143-869B- lower Paleocene Zone NP4 and lower Maastrichtian Zone CC23 of 5R-1, 94 cm. A major unconformity, which includes upper Paleocene Sissingh (1977). Precise zonal assignment is difficult in the Upper Zones NP9 to NP5, lies in the lower part of Core 143-869B-5R. The Cretaceous sequence as a number of the Sissingh (1977) markers, next dated sample, from Section 143-869B-6R-1, belongs to the including Reinhαrdtites αnthophorus, Reinhαrdtites levis, Cαlculites middle Paleocene Zone NP4. This assignment is based on the occur- obscurus, Luciαnorhαbdus cαyeuxii, Luciαnorhαbdus mαleformis, and rences of early species of Fαsciculithus, including Fαsciculithus Microrhαbdulus decorαtus, are missing or very rare. In the following

318 SITE 869

Core 23R „ Core 25R Core 26R Core 27R .Core 31R Core 32R Core 33R Core 34R Core 35R Core 36R 0 T 0T

100- 100i cm

cm

Te, pelagic sedimentation Ta, massive, graded, very coarse-grained

Td, upper parallel laminae Grain and debris flows

Tb and Tc, wavy and plane parallel laminae Slump

Ta, massive, graded, coarse-grained

Figure 23 (continued). discussion, we therefore rely on the ranges of a number of secondary ssp. parca, suggests an earliest Campanian to Santonian age within markers. Samples 143-869B-8R-CC through -10R-CC have been Zones CC16 or CC17. An unconformity, which includes the upper assigned to uppermost Campanian to lower Maastrichtian Zones Coniacian to Santonian Zones CC14 to CC15, lies in between Sec- CC22 to CC23, based on the occurrence of primary marker Quadrum tions 143-869B-30R-CC and -31R-1. trifidum and secondary markers Quadrum gothicum and Quadrum Coniacian Zone CC13 correlates to Sections 143-869B-31R-1 to sissinghi. The subsequent interval between Samples 143-869B-11R- -32R-3, based on the combined occurrence of primary marker M. fur- CC and -16R-CC lies in upper Campanian Zone CC21, as suggested catus and Q. gartneri and the absence of primary marker M. decussata. by the occurrence of secondary markers Q. sissinghi and Q. gothicum, Sections 143-869B-33R-1 to -35R-CC lie in Turonian to lower Ceratolithoides aculeus, and Ceratolithoides verbeekii and the ab- Coniacian Zones CC11 to CC12, as indicated by the presence of sence of primary marker Q. trifidum. Based on the presence of second- Eijfellithus eximius and the absence of M. furcatus and M. decussata. ary markers C. aculeus and C. verbeekii, and the absence of second- The remainder of the sequence from Core 143-869B-36R through ary markers Q. sissinghi and Q. gothicum, the interval between Sam- -69R is of middle to late Cenomanian age and correlates to Zones CC9 ples 143-869B-17R-1,100 cm, and -19-CC has been assigned to upper to CC10. Distinction between these zones is not possible because the Campanian Zone CC20. marker Microrhabdulus decoratus has not been observed in this It is difficult to date the interval between Samples 143-869B- interval. This age is based on the occurrence of Corollithion kennedyi 20R-1, 70 cm, and -21R-CC owing to poor preservation. All of the throughout the sequence and of Lithraphidites acutus in the interval traditional marker species are absent, extremely rare, or very over- between Samples 143-869B-46R-1, 35 cm, and -66R-3, 14 cm. grown. Based on the absence of primary marker Q. sissinghi, this Whereas L. acutus is limited to the upper Cenomanian Zone CC10, interval has been tentatively assigned to lower Campanian Zones the range of C. kennedyi extends down through the Cenomanian. CC18 to CC19. Samples 143-869B-22R-1,46 cm, to -25R-CC belong Eiffellithus turriseiffelii, which has its first occurrence in the latest to Subzones CC18b and CC19a, based on the occurrence of primary Albian, is common throughout the sequence. Other species that last marker Bukryaster hayi, Q. gothicum, and rare C. verbeekii. Sections occur in the Cenomanian, including Rhagodiscus asper, Micro- 143-869B-16R-1 through -28R-CC are in the lowermost Campanian stauus chiastius, and Axopodorhabdus albianus, have been found in Zone CC18, based on the occurrence of rare primary marker Broin- numerous samples. In the volcaniclastic sediments, nannofossils are sonia parca ssp. parca, Q. gothicum, Lithraphidites grillii, and the most commonly found in interbedded claystones and are rare or absence of primary marker Marthasterites furcatus. Samples 143- absent in coarser lithologies. 869B-29R-CC and -30R-CC contain M. furcatus and secondary The source of nannofossils in these sediments is open to question. markers Micula decussata, Quadrum gartneri, and Lithastrinus gril- It is likely in most of the Cretaceous sequence that nannofossils are of lii. The co-occurrence of these species, and the absence of B. parca pelagic origin because there is no likely hemipelagic source upslope.

319 SITE 869

Core38R Core 39R Core 40R Core 41R Core 42R Core 43R Core 44R Core 45R Core 46R Core 50R u : U . i* if •if • '!**! if

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200ijj io n 2 1 io n o 1ü I Φ Φ Sec t CO CO • • 1 1 - • 1 1 CO 300" I CO 300-j| 300-β - 1- 300-fl 300" cm • ü co cti i Φ p Φ CO c •I 4 CO - •if •if g "ö~

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400- 400-B Sect i 400": 400- cm — - *•!*• I P •f••*• I- 1 o Φ io n 4 s 3 CO 500^ 500-3• 500-d•

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*!*- Iu 1 Φ mI *•!* CO — *••*• ; -ki•müS8a fT m *• *• LD c *•!*• U 600"^ 600-SI - 6Oθ4| •2 cm : cm 9 Ü 600- • CΦO

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scti c ü CO I •ü 700^ "ü" cm j o 700-

Te, pelagic sedimentation Ta, massive, graded, very coarse-grained

Td, upper parallel laminae Grain and debris flows cm

Tb and Tc, wavy and plane parallel laminae Slump

Ta, massive, graded, coarse-grained

Figure 23 (continued).

However, in Cenozoic sediments, it is possible that nannofossils were Foraminifers redeposited in the distal parts of turbidite fans. This would explain their preservation at paleodepths below the CCD and the absence of Hole 869A foraminifers in many intervals as a result of sorting. Planktonic foraminifers from Hole 869A are limited to the lower Palynomorphs Oligocene in Cores 143-869B-4H to -8H. Assemblages consist of rare-to-abundant, poorly to moderately well-preserved specimens. Samples 143-869A-1H-CC and -869B-34R-CC, 9-10 cm, were Washed residues from Cores 143-869A-1H to -3H and -9H to -15H processed for palynology and found to be barren. Other samples were are devoid of foraminifers and instead contain poorly preserved radio- not processed for palynology after visual inspection and organic larians, with the addition of sponge spicules in the lower cores. geochemical analyses of the cores indicated little reason to expect any The Oligocene sequence ranges from Zones P20/21 down to Zone recoverable palynomorphs. PI 8, in apparent stratigraphic continuity, with the exception of a rede-

320 SITE 869

. Core 51R Core 55R „ Core 56R Core 57R

100-

200- 200-

300-

400- cm

8001 cm

Te, pelagic sedimentation Ta, massive, graded, very coarse-grained

Td, upper parallel laminae Grain and debris flows

Tb and Tc, wavy and plane parallel laminae Slump

Ta, massive, graded, coarse-grained

Figure 23 (continued).

321 SITE 869

Core 61R Core 63R Core 64R Core 65R Core 66R Core 67R Core68R Core 69R Core69R

100-i 100-

20(H 200-

CO

30C 300- 300-

400- 400-

Lo 500- 500-

600- 600-

700- 70C

800- 800 cm :

900- cm f%Uo o

>•>•>•s Te, pelagic sedimentation Ta, massive, graded, very coarse-grained

Td, upper parallel laminae Grain and debris flows

Tb and Tc, wavy and plane parallel laminae Slump

Ta, massive, graded, coarse-grained

Figure 23 (continued).

322 SITE 869

Age Intervals Max. Max. Sub- cm :Core TOC thickness units 200-1 0 50 100200 err Interpretation Fining-upward 26- sequences locally pro- grading over thin silty tur- 27- >idites: middle fan deposits: channel fills 300- MA 28- and overbank fines Slumps in- dicate affinity 29- to inner fan deposits 30 - Ibuterfan Very thin Figure 25. Contact between Subunits HIE and IIIF, where a coarse volcaniclas- 400 turbidites: tic mass flow overlies fine-grained Td intervals. Note traction carpet at base Basin plain of grain-flow unit (arrows) (Interval 143-869B-55R-2, 25-30 cm). ~ Té^Td NIB couplets posited older assemblage in Sample 143-869A-4H-3, 80-82 cm. The frequent: latter assemblage from a turbidite layer consists of "Turborotalia" Outer fan Middle fan_ ampliapertura, Subbotina gortanii, "Globigerina " tapuriensis, and NIC Pseudohastigerina micra, which characterize Zone PI8. The sample Outer fan also contains redeposited bryozoan fragments, larger benthic fora- Grain flow fills minifers, small calcareous benthic foraminifers, ostracodes, echi- :500- and debris noid spines, bivalve fragments, and radio- larians, in addition to flows: channe HID fills and inner in-situ agglutinated abyssal foraminifers and fish debris. Sample fan 143-869A-4H-CC is younger and was assigned to Zones P20/21 by the presence of Paragloborotalia opima, "Globigerina" ciperoen- Inner fan sis, G. venezuelana, Globigerina tripartita, and Catapsydrax dis- Middle fan similis. This assemblage continues downhole to Sample 143- 869A-5H-CC. The occurrence of "Turborotalia" ampliapertura, Turborotalia 600- HIE Grain flows pseudoampliapertura, and Subbotina angiporoides in Sample 143- and debris 869A-6H-CC indicates Zones PI9/20. This is followed by the over- flows: lap of Globigerina sellii, Pseudohastigerina sp., and Cassigerinella Inner fan chipolensis in Sample 143-869A-7H-CC that defines a stratigraphic position within Zones P18 and P19. Finally, Sample 143-869A- 8H-CC has been preliminarily referred to Zone PI 8 by the presence Thick but of very poorly preserved "Turborotalia" ampliapertura, Subbotina relatively fine- grained Ta praeturritilina, and Paragloborotalia opima nana, among others. 700- intervals, Biogenic constituents in the Oligocene sequence, with the excep- fining up- tion of the sample from the turbidite layer in Core 143-869A-4H, are ward intoTc-T characterized by agglutinated foraminifers, fish debris, and radiolar- INF couplets: ians, consistent with deposition at abyssal water depths. Preservation Middle fan of the lower Oligocene planktonic foraminifers at these depths and with high the absence of foraminifers in the radiolarian-dominated older and sediment younger Cenozoic sediments may be related to passage of the site supply beneath the equatorial zone of high productivity caused by plate Middle to motion, perhaps augmented by the decrease in CCD near the Eo- ING 800-1 outer fan cene/Oligocene boundary (Berger et al., 1981). Ta-Te Bouma turbidite intervals 2 Slumps G Grain and debris flows © Shallow-water debris Hole 869B • Dominant intervals © Chert • Important intervals Because of poor recovery owing to the presence of porcellanite and Intervals present chert, Cenozoic planktonic foraminifers from Hole 869B have been limited in Cores 143-869B-1R to -10R to Eocene assemblages identi- Figure 24. Summary diagram of the observed sedimentary features in Unit fied in thin section from limestone in Core 143-869B-4R. The sparse III and interpretation of the corresponding depositional environments. Rela- and poorly preserved fauna consists of Morozovella aequa, Morozor- tive abundance of mass-flow intervals and maximum thicknesses have been ellaformosa, Morozorella marginodentata, Muricoglobigerina solda- plotted for the upper and lower halves of recovered material in each core; doensis, Pseudohastigerina, and Planorotalites sp. cf. P. chapmani where only one section was recovered, only one plot was made. Cores having that yield an early Eocene age (Zones P6c-P7). Elements of this assem- less than 50 cm of recovered material were not considered. Note the change blage occur in Samples 143-869B-4R-1, 48-51 cm, 82-84 cm, along of scale at 100 cm in the maximum-thickness column. Thicknesses of grain with rare calcareous benthic foraminifers and volcanogenic debris. and debris flows may reach several meters. The values of total organic carbon (TOC) have been plotted only where they significantly exceed a background value of 0.2% to 0.3%. 323 SITE 869

C S fScSvcS G i i i i i i B, Bottom of a thick decametric- scale sequence set. First meter- 550 scale sequences consist of very coarse sandstone and very coarse sandstone with granules. C S ts cS i I i Decimetric-scale Ta-Te e - d —I or Tb-Te Bouma E ed •= = ^ o c sequences are LD e. ... * CM : •• " " " " c -—<\ •• .•:•:•••: generally followed by thin metric-scale c s fS cS Tc-Te or Td-Te I 1 e i v sequences, which may represent - middle-fan levee or F c o interchannel deposits. in 10 m-

b | In each unit, plurimetric c s fS cS coarse-grained basalt sequences are followed Very coarse sandstone with e by metric- to decimetric- granules (G) d \ ;—_ scale Ta-Te, then Tb-Te Very coarse sandstone (vcS) A, Top of a thick Bouma sequence sets. Coarse sandstone (cS) decimetric- c *> \ N. Thinning-up and fining | Fine sandstone (fS) scale sequence up sequence sets may

b m 1 | Siltstone (S) and claystone (C) consisting of represent middle fan Ripples and small-scale cross several thinning- F channel infilling. and fining-upward Ü a bedding X) Parallel laminations sequences. C\J 0 m

Figure 26. Schematic representation of mass-flow sequences typical of Subunit HIE, based on observations from Sections 143-869B-50R-1 to -52R-2.

Cretaceous planktonic foraminifers, identified in both washed radiolarians and sponge spicules. A more abundant and diverse samples and thin section, were found in Cores 143-869B-1 OR to -52R assemblage of early Coniacian age {Dicarinella primitiva Zone) and range from Maastrichtian to late Cenomanian in age. Specimens appears in Sample 143-869B-31R-1, 72-7r4 cm. Present are Margi- are mostly rare to few in abundance and characteristically poor in notruncana sigali, Marginotruncana schneegansi, Marginotrun- preservation owing to calcite dissolution. Maastrichtian planktonic cana pseudolinneiana, Dicarinella primitiva, Dicarinella imbri- foraminifers were found in Samples 143-869B-10R-CC and -11R-1, cata, Whiteinella baltica, Whiteinella aprica, and Praeglobotrun- 4-6 cm, and consist of Globotruncanita stuarti, Globotruncanita cana gibba, among others. Associated with these species are re- stuart if or mis, Globotruncanita elevata, Globotruncana linneiana, worked middle to upper Cenomanian forms, such as Rotalipora questionable Globotruncana aegyptiaca, and Contusotruncana for- cushmani and Rotalipora greenhornensis. Redeposited material in- nicata, among others. Both samples contain larger benthic foramini- cludes ooids, gastropods, echinoid spines, Inoceramus prisms, os- fers (e.g., orbitoidids), whereas the latter sample also contains ooids, tracodes, sponge spicules, and small calcareous benthic foraminifers. bivalve fragments, and echinoid debris. Lower to middle Turonian planktonic foraminifers (Helvetoglo- Planktonic foraminifers of Campanian age were found in Samples botruncana helvetica Zone) occur in Samples 143-869B-34R-1, 143-869B-11R-CC to -28R-CC and include Globotruncana area, 142-144 cm, and -35R-1, 44-46 cm. In addition to the nominate Globotruncana bulloides, Globotruncana mariei, Globotruncana species, the assemblage includes Dicarinella algeriana, D. imbri- subspinosa, Globotruncana orientalis, Globotruncana ventricosa, cata, Dicarinella canaliculata, Dicarinella hagni, Prae globotrun- Globotruncanita stuartiformis, Contusotruncana fornicata, and Con- cana gibba, and Marginotruncana sigali., among others. Associated tusotruncana patelliformis, among others. The presence of Globotrun- redeposited material includes ooids and coated grains, bivalve and cana ventricosa in Core 143-869B-28R, adjacent to older planktonic echinoid fragments, sponge spicules, and both calcareous and agglu- foraminifers in Core 143-869B-30R, suggests the presence of an tinated benthic foraminifers. unconformity that involves much of the early Campanian age Glo- Upper Cenomanian planktonic foraminifers first appear in Sample botruncanita elevata Zone. Other biogenic material in the Campanian 143-869B-36R-3, 13-14 cm, and continue downhole to Sample 143- samples includes redeposited neritic and bathyal smaller calcareous 869B-52R-5, 12-15 cm. The fauna is representative of the Dicari- benthic foraminifers, bryozoans, bivalve and echinoid fragments, nella algeriana Subzone of the middle to late Cenomanian age Rota- sponge spicules, and radiolarians, as well as in-situ fish debris and lipora cushmani Zone and includes both nominate species, plus Rota- agglutinated abyssal foraminifers. Redeposited ooids are restricted to lipora deeckei, Rotalipora greenhornensis, Prae globotruncana del- Samples 143-869B-19R-CC, -20R-CC, and -25R-1, 43-45 cm. rioensis, Prae globotruncana stephani, Whiteinella aprica, and Het- Older planktonic foraminifers appear in the siltstone of Core 143- erohelix moremani. Redeposited material includes rare ooids, gastro- 869B-30R. The assemblage of very small, size-sorted specimens in- pods, echinoid spines, larger and smaller calcareous benthic foramin- cludes Heterohelix moremani, Heterohelix reussi, Hedbergella ifers, and radiolarians mixed with in-situ abyssal benthic foraminifers. planispira, and Globigerinelloides sp. and supports an age no younger Planktonic foraminifers and redeposited calcareous material be- than Santonian. This assemblage is associated with poorly preserved come increasingly sparse downhole in the coarse grain and debris

324 SITE 869

cm 64

66-

Meter-scale fining- and 68- thinning-upward sequence: Channel fill

70-

72- Thin Tc-Td couplets: Overbank fines

Ta 74- Figure 28. Schematic sequences typical of Subunit IIIA. For discussion refer to text.

the radiolarians and calcareous nannofossils, if not related to differ- ential dissolution, then is perhaps primary and related to changes in 76- the upper-water column caused by the continued volcanism that modified the pelagic habitats. PALEOMAGNETISM APC Cores

78 -> The archive halves of Cores 143-869A-1H through -9H were measured with the pass-through cryogenic magnetometer at a spacing Figure 27. Two Tc-Td couplets typical of the lower part of Subunit IIIB. Note of 5 cm. After measuring natural remanent magnetization (NRM), we soft-sediment deformation in the lower Tc interval and current ripple in the subjected the cores to alternating-field (AF) magnetic "cleaning" at upper one (Interval 143-869B-31R-1, 64-78 cm). 15 mT. Whole-core magnetic-susceptibility measurements were per- formed using the MST. flows of Cores 143-869B-38R to -57R and are then succeeded by NRM intensities varied on the order of 0.1 to 1000 mA/m, and radiolarians to the bottom of the hole. The lowest occurrence of intensity peaks tended to occur within the top 40% to 50% of each planktonic foraminifers is in Sample 143-869B-57R-2, 122-125 cm, core, with a pattern similar to that which was typical of the APC cores and consists of extremely small, thin-walled hedbergellids associated from Site 865. The upper-core intensity peak varies in magnitude from with radiolarians in volcaniclastic siltstone. That these dissolution 10 to 1000 times the intensity values in the lower sections, and susceptible specimens are preserved with radiolarians suggests that magnetic directions are erratic. Three possible causes of this observed dissolution below the CCD was not the sole reason for the lack of disturbance are (1) rust contamination, (2) drill-string overprint, and planktonic and calcareous benthic foraminifers. The presence of (3) physical disturbance resulting from the coring process. The lower radiolarians in graded layers and thin laminae associated with size- densities at the core breaks seen in the GRAPE data (see "Physical sorted volcaniclastic material throughout the Cenomanian sequence, Properties" section, this chapter) may indicate some possible physical and especially noticeable in Cores 143-869B-68R and -69R, attests disturbance at the top of the core that resulted during coring. to the redeposited nature of these deposits. Presumably, the absence In the report for Site 865, we suggested that rust contamination of shallow-water material and neritic benthic foraminifers reflects a (Sager, 1986, 1988; Tarduno et al, 1991) could be a possible cause volcanic source at deeper water depths. Following this argument, the of the abnormally high intensities observed in the upper sections of absence of bathyal benthic foraminifers is evidence of rapid and the cores. At this site, we observed large (>l mm) rust flakes between continued sedimentation that overwhelmed the deeper-water benthic the sediment and the core liner in the top sections of highly magnetic communities. The exclusion of planktonic foraminifers, in contrast to cores. We also detected smaller rust flakes in smear slides of the

325 SITE 869

cm Nannofossils Foraminifers

36- Cor e n 1H lower 38- 2H NN2 Miocene 3H 40- 4H NP24 u. Olig. H P18 I. Oligocene

5H P20 - P21 I. Oligocene 42- NP23 50- 6H lower -|P19-P20 I. Oligocene 44- 7H Oligocene P18 I. Oligocene 8H NP21 Te 46- 9H NP20 10X upper 48- Eocene 100- 11X NP18-NP19 Td 12X NP16-NP17 50- middle 13X Eocene NP15 52- 14X

15X NP13-NP14

54- 150- 16X

17X 56- 18X

58- Figure 30. Cenozoic nannofossil and planktonic foraminiferal biostratigraphy of Hole 869A. Martini's zones (1971) are illustrated for the hole as well as corresponding epochs. Abbreviations: u. = upper; 1. = lower. 60- sediments taken near the core liner, even in the few cores that seemed less affected. 62- Magnetic Polarity Stratigraphy As a result of drilling disturbance, we were unable to resolve a 64- reliable magnetostratigraphy from the whole-core measurements of the archive halves of the APC cores. Because the rust seems tb be confined to the outside of the core between the core liner and the core 66- itself, it may be possible to extract reliable magnetostratigraphic data using a discrete-sampling program.

Magnetic Susceptibility

The range of magnetic susceptibility readings is on the order of 0 70- Tb to 1000 µcgs, with the highest susceptibilities at the top of each core (Fig. 32). These peaks correspond to the peaks in magnetic intensity mentioned earlier. The low values of susceptibility between 35 and 72 -1 75 mbsf correspond to a section having high percentages of (see "Organic Geochemistry" section, this chapter), which Figure 29. Stacked Tb-Td-Te intervals in the upper part of a fining-upward suggests dilution of this section by calcium carbonate. channel-fill sequence. Td intervals are dark-colored by clays. Bioturbation partly mixed the fine turbiditic and the light-colored pelagic sediment (Interval 143-869B-13R-2, 35-72 cm). RCB Cores RCB coring at Hole 869B resulted in the recovery of long, continuous core segments, beginning with Core 143-869B-19R, that

326 SITE 869

Nannofossils Foraminifers Nannofossils Foraminifers Cor e Cor e 1 450- 34 CC11 -CC12 Turon. m. Turon. 2 35 loU 3 36 4 — I. Eoc. 37 NP10 I. Eoc. c 38 6 NP4 u. Pal. 500- 39 7 40 200- 8 41 9 I. Maas.- 42 CC22 CC23 upper 10 u. Camp. 43 Cenomanian Maas. 11 550- 44 12 45 250- 13 upper 46 CC21 14 Campanian 47 15 48 16 600- 49 upper 17 50 CC10 Cenomanian -Q E 300- 18 CC20 51 m. - u. 19 52 Cenomanian CD 20 Campanian a 53 21 54 650- 22 lower 55 CC18-CC19 Campanian 350- 23 56 24 57 25 58 26 59 27 CC18 60 28 61 .inn 29 I. Camp.- 62 CC16-CC17 30 u. Sant. Sant. 63 31 I. Coniac 64 CC13 I. Coniac 32 /bU- 65 33 66 450- I. Con.- 34 CC11 -CC12 67 Turon. m. Turon. 35 68 m.-u. CC9-CC10 Cenomanian 36 CC10 u. Cen. u. Cen. 69

Figure 31. Cenozoic and Cretaceous nannofossil and planktonic foraminiferal biostratigraphy of Hole 869B. Abbreviations: u. = upper; 1. = lower. were suitable for measuring with the pass-through cryogenic magne- zation at 15 mT, the most continuous pieces have inclinations that are tometer. Measurements were taken at a 5-cm interval of the NRM and positive, but scattered and typically range from +10° to +40°. remanence after demagnetization at 15 mT. The raw data obtained by 3. Unit 3 (Cores 143-869B-34R to -69R). This unit is characterized these pass-through measurements contain numerous edge effects, by small changes in direction with demagnetization. The most con- which are created when two separate core pieces, having different tinuous pieces have inclinations of between -30° and -40° after azimuthal orientations and hence declinations, are measured. Ac- demagnetization at 15 mT. counting for these spurious values, the pass-through measurements can be used to divide the column into the following magnetic units: In Cores 143-869B-27R to -33R, recovery was not sufficient for meaningful pass-through measurements; thus, this interval has been l.Unit 1 (Cores 143-869B-19R to-20R). This unit is characterized omitted from the classification. by small changes in direction with AF demagnetization. The most The demagnetization behavior exhibited by paleomagnetic Unit 2 continuous pieces (i.e., in Core 143-869B-19R) have inclinations is similar to that observed in paleomagnetic studies of pelagic sedi- after 15 mT demagnetization of between -10° and -30°. ments from other Pacific Ocean sites (e.g., Site 167, Magellan Rise, 2. Unit 2 (Cores 143-869B-21R to -26R). This unit is characterized seeTardunoetal., 1989). Specifically, the data most closely resemble by large changes in direction with demagnetization. After demagneti- the situation when a present-day overprint (having a positive inclination)

327 SITE 869

Volume magnetic Sample 143-869B-34R-2, 96-98 cm susceptibility (µcgs) W, up 0.1 1 10 100 1000 NRM

Div. = 5.0e+1 (mA/m) E, down .

Volcaniclastic claystone (Td), normal polarity

Figure 33. Orthogonal vector plot (left) of progressive AF demagnetization of volcaniclastic claystone (Sample 143-869B-34R-2, 96-98 cm). Open circles = inclination; closed circles = declination (unoriented); large circles = natural remanent magnetization (NRM); small circles = vector end points after demag- netization (labeled in mT). Demagnetization steps shown (mT): 0, 2.5, 5.0, 10.0, 15.0, 20.0, 30.0, 40.0, 50.0, 60.0, 80.0. Stereonet plot (right) of vector end points after progressive AF demagnetization.

Sample 143-869B-32R-1, 14-16 cm

W,up " NRM 150

Figure 32. Volume-magnetic susceptibility plotted with depth for Hole 869A. Horizontal lines indicate core breaks.

is removed from samples having a primary reversed-polarity mag- netization (having a negative inclination) acquired in the Southern Hemisphere. The differences in both inclination and declination between the present-day-field overprint and the primary direction are reflected by large changes in direction with AF demagnetization. Paleontological age assignments (see "Biostratigraphy" section, this chapter) place paleomagnetic Unit 1 in the early Campanian E, down Div. = 1 .Oe+2 (mA/m) (nannofossils), Unit 2 in the early Campanian (nannofossils) and Unit 3 in the Turonian to Cenomanian (nannofossils and foramini- Brown claystone, normal polarity fers). Based on analogy with the demagnetization behavior observed in previous studies (Tarduno et al, 1989) and the standard biostrati- Figure 34. Orthogonal vector plot (left) of progressive AF demagnetization of graphic correlation of geologic stage with polarity chron (Kent and a brown claystone (Sample 143-869B-32R-1, 14-16 cm). Plot conventions as Gradstein, 1985), the simplest magnetostratigraphic assignment of in Figure 33. the paleomagnetic units is as follows: Unit 1 records the lower portion of C33N; Unit 2 represents C33R, and Unit 3 represents the upper to zation is also an adequate technique for isolating the characteristic middle portion of the Cretaceous normal polarity superchron (K-N). remanent magnetization for brown claystone samples (Fig. 34) in the To test whether the pass-through measurements accurately record poorly recovered interval between Units 2 and 3. High-coercivity the primary geomagnetic polarity, discrete samples were collected ferromagnetic minerals, which might be associated with the brown from paleomagnetic Units 2 and 3 and subjected to step-wise demag- coloration, apparently are not the major contributor to the remanence. netization. Discrete samples were also collected from the poorly Measurement of these brown claystones indicates that the normal recovered interval between Units 2 and 3. The discrete samples were polarity that characterizes Unit 3 extends upward to at least Core demagnetized up to 20 mT using the pass-through AF demagnetiza- 143-869B-32R. tion system; higher AF demagnetization steps were applied with the Some samples from paleomagnetic Unit 2 have a demagnetization Schonstedt AF demagnetizer. In many samples, the intensities after behavior that differs greatly from that displayed by the samples from application of 20 mT (with the pass-through demagnetizer) are essen- paleomagnetic Unit 3. Such samples show a large angular difference tially identical to those after demagnetization of 30 mT (with the between the NRM and vector end point after demagnetization at Schonstedt system), which suggests a calibration problem with one relatively high peak AFs (60-80 mT) (Fig. 35). This behavior is (or both) system(s). The vector end point directions are also essen- similar to that observed at other Pacific Ocean sites, where a present- tially identical, indicating that this calibration discrepancy does not day overprint has been removed from a sample having a primary affect the accuracy of the directional data significantly. reversed-polarity component, as discussed above. A great circle path Demagnetization of volcaniclastic sediments from paleomagnetic is defined by the vector end points (Fig. 35) and marks the vector track Unit 3 reveals a single component of magnetization, which trends to of a normal-polarity overprint-declination value to a reversed-polarity the origin of orthogonal vector plots after the removal of a minor, primary-declination value. The angular difference between the NRM low-inclination component (Fig. 33). Interestingly, AF demagneti- and primary direction differs from 180° by only the small rotation of

328 SITE 869

Sample 143-869B-23R-1, 60-62 cm W, up .2.5

Div. = 1.0e+1 (mA/m) E up

Volcaniclastic sandstone (Tb-Tc), reversed polarity

Figure 35. Orthogonal vector plot (left) of progressive AF demagnetization of volcaniclastic Sample 143-869B-23R-1, 60-62 cm. Demagnetization steps shown (mT): 0, 2.5, 10.0, 15.0, 20.0, 30.0, 40.0, 50.0, 60.0. Other plot conventions as in Figure 33.

Sample 143-869B-26R-1, 54-56 cm W, up NRM N

40 60 80 100 Age (Ma)

Figure 37. A. Age vs. depth plot for Site 869. B. Sedimentation rate vs. age for Site 869. Unconformities denoted by "u" (see text for details).

on the pass-through cryogenic magnetometer measurements. In no interval was any evidence for reversed polarity observed. This ship- E, down Div. = 2.5e+1 (mA/m) board survey lends further support to the suggestion that previously reported intervals of brief reversed polarity in Cenomanian sediments Volcaniclastic claystone (Td-Te), reversed polarity from the Ruhr area of Germany (Hambach and Krumsiek, 1989) result Figure 36. Orthogonal vector plot (left) of progressive AF demagnetization of instead to overprinting in a Matuyama (or late Tertiary) field (Tarduno volcaniclastic claystone Sample 143-869B-26R-1, 54-56 cm. Demagnetiza- etal., 1992). tion steps shown (mT): 0, 2.5, 10.0, 15.0, 20.0, 30.0, 40.0, 50.0, 60.0. Other plot conventions as in Figure 33. SEDIMENTATION RATES Figure 37 shows the depth-vs.-age plot and sedimentation rates the Pacific Plate since the Late Cretaceous and by inadequacies in the for the Cenozoic and Cretaceous section recovered in Holes 869A and AF cleaning (see Tarduno et al., 1989 for discussion). Other samples 869B. The ages used in calculations are based on nannofossil zonal from paleomagnetic Unit 2 display a simpler demagnetization behav- boundaries taken from the Berggren et al. (1985) time scale for the ior, similar to that displayed by the discrete samples from paleomag- Cenozoic and from the Kent and Gradstein (1985) time scale for the netic Unit 3, but having an inclination of opposite sign (Fig. 36). Cretaceous. In Figure 37A, sub-bottom depth has been plotted vs. age. In summary, data from the discrete samples indicate that the pass- This plot shows the position of four postulated unconformities. These through measurements are an accurate measure of polarity and confirm include (1) the top of Hole 869A, where we spudded into lower the correlation of magnetic units with polarity chrons. Differential Miocene sediments, (2) across the Oligocene/Miocene boundary, overprinting of the present-day field, as observed in the discrete (3) the upper Paleocene; and (4) the Cretaceous/Tertiary boundary. samples, most likely explains the scattered inclination values observed The latter unconformity includes part of the lower Paleocene and in the pass-through measurements of paleomagnetic Unit 2. This much of the Maastrichtian. Kent and Gradstein's time scale (1985) differential overprinting is probably related to lithology. For example, does not give ages for several of Sissingh's zonal markers (1977), a volcaniclastic claystone (Te) shows only a minor overprint compo- which we used to date the section. Thus, this plot shows less detail nent (Fig. 36), while a coarser- grained volcaniclastic sample (Tb-Tc) than is apparent from our preliminary biostratigraphic investigations. displays a large overprint component (Fig. 35). The available data Missing also from the section is much of the Santonian and part of suggest that the coarser-grain lithologies may record a more substantial the Coniacian at an unconformity at the base of Core 143-869B-30R. overprint, perhaps reflecting a greater range of magnetic grain sizes. Figure 37B shows a plot of age vs. sedimentation rate for Further shore based studies will be needed to test this suggestion. Holes 869A and 869B. This illustrates somewhat variable rates of The relatively simple magnetic behavior exhibited by the discrete deposition in the lower Miocene and Paleogene part of the section, samples from paleomagnetic Unit 3, the high sedimentation rates between 0.7 and 17 m/m.y. Some of this variation may be derived from implied by the biostratigraphic data (see "Biostratigraphy" section, the nondetailed sampling that forms the basis of this analysis or from this chapter), and the continuity of the recovered turbidite cores our assumption that certain zones are complete in these holes, whereas permits a near-continuous evaluation of magnetic polarity for most they may be only partly represented. Note that average Cenozoic of the upper Cenomanian and part of the middle Cenomanian, based sedimentation rates are higher than in the contemporaneous part of

329 SITE 869

Site 865, on the summit of Allison Guyot. This may result from the Alkalinity andpH large flux of radiolarians at this site or from the possible downslope redeposition of part of the sediment fraction, including nannofossils. The alkalinity and pH measurements have mean values of 3.15 ± Figure 37B differentiates the sedimentary environments that led to 0.3 and 7.68 ± 0.07 in Hole 869A and 0.68 ± 0.3 and 7.77 ± 0.45 in the deposition of the Cretaceous section in Hole 869B. Campanian Hole 869B, respectively. The major trend in the alkalinity and pH turbiditic sediments were deposited at rates between 15 and 30 m/m.y., values throughout both holes indicates that alkalinity decreases dra- whereas rates between 4 and 9 m/m.y. characterized hemipelagic matically with depth and pH increases slightly. This change in pore- deposition. The sedimentation rate of 60 m/m.y. calculated for the water chemistry is associated with the lithologic change between the middle and upper Cenomanian volcaniclastic deposits is a minimum nannofossil and radiolarian oozes in Hole 869A and the volcani- estimate that assumes: (1) a Cenomanian/Turonian boundary age of 91 clastic-dominated facies in Hole 869B. The large decrease in alka- Ma, (2) that we actually identified the first occurrence of Lithraphidites linity is related to the decrease in cations in the pore waters within acutus in Core 143-869B-66R, and (3) that the age given for this datum the volcaniclastic sediments (Table 3). Superimposed on the major by Kent and Gradstein (1985) is accurate. In fact, recent age estimates alkalinity change (between Holes 869A and 869B), is a subtle trend for the Cenomanian/Turonian boundary lie close to 93 Ma (J.D. toward increasing alkalinities within Hole 869A, which may be Obradovich, pers. comm., 1992). In addition, because L acutus has a related to organic carbon degradation. patchy occurrence in this hole, it is possible that its range extends down to the base of the section. Finally, the age of this datum given by Kent Calcium, Magnesium, Sodium, Potassium, and Gradstein (1985) is probably a little old. Therefore, it is not Strontium, and Rubidium unreasonable to suppose that the entire Cenomanian section was deposited in 1 m.y. or less at rates close to 300 m/m.y. Concentrations of the cations that were measured in Holes 869A and 869B all show significant downhole changes. Calcium concen- INORGANIC GEOCHEMISTRY trations are near that of seawater in Hole 869A (10.7 ± 0.4 mM), but increase to a maximum of 190.6 mM in Sample 143-869B-31R-1 Interstitial Waters (Table 3; Fig. 38). Magnesium concentrations are near that of sea- water in Hole 869A (53.3 ± 0.48), but decrease through Hole 869B Interstitial waters were taken from 15 core samples in Holes 869A to a minimum of 4.4 mM in Sample 143-869B-31R-1 (Table 3; and 869B and analyzed according to the methods outlined in the Fig. 38). The average change between Holes 869A and 869B is "Explanatory Notes" chapter (this volume). Five of these samples 1017% or a 98.1 mM increase for calcium and 77% or a 41.3 mM came from Miocene to Eocene nannofossil and radiolarian oozes in decrease for magnesium. Hole 869A, and 10 samples from the volcaniclastic-dominated strata of Campanian age in Hole 869B (Table 3). The sodium concentrations in Hole 869A are near seawater values (473 ± 28 mM), but decrease by 24% or 112 mM to a mean of 361 ± Salinity and Chlorinity 97 mM in Hole 869B. Similar trends occur in the potassium concen- trations: pore-water potassium concentrations are similar to those of Pore-water salinities in Holes 869A and 869B range from 35 to seawater in Hole 869A (10.4 ± 0.5), but decrease to a minimum of 41‰ . Samples from the upper 420 mbsf have salinities that are similar 0.5 mM in Hole 869B. This decrease in potassium is, on average, to seawater, whereas samples from 691.5 mbsf and below have salin- 8.8 mM or 85% between Holes 869A and 869B. Strontium concen- ities of 39 to 41‰ (Fig. 38). Chlorinity values are similar to those of trations increase from 75 µM in the uppermost sample of Hole 869A seawater throughout both holes (547-591 mM Cl"; Fig. 38). A mini- to a minimum of 291 µM in Hole 869B. A sharp increase occurs at mum chlorinity value of 547 mM Cl" was measured in the sample the break between Holes 869A and 869B. Rubidium concentrations from Section 143-869B-20R-2 with a maximum value of 591 mM in decrease from 1.84 µM in the uppermost sample of Hole 869A to the sample from Section 143-869B-59R-1. 0.17 µM in the deepest measurement from Hole 869B.

Table 3. Interstitial-water data from Holes 869A and 869B.

+ + + 2+ 4+ 2+ 2+ Core, section Depth Water Salin. K Na Rb Sr cr PO4 NH4 Si so4 Ca Mg interval (cm) (mbsf) (mL) pH Alkal. (‰) (mM) (mM) (µM) (µM) (mM) (µM) (µM) (µM) (mM) (mM) (mM)

Hole 869A

1H-5, 145-150 7.5 72.0 7.75 2.87 36.0 10.93 466. 1.84 75. 556. 1.60 8. 442. 27.41 10.6 53.0 4H-5, 145-150 36.2 40.0 7.60 3.07 36.0 10.44 469. 1.83 75. 564. 1.97 13. 569. 27.00 10.4 53.9 7H-5, 145-150 63.3 26.0 7.60 3.09 36.0 10.27 469. 1.77 76. 568. 2.35 22. 726. 26.76 10.7 53.5 10X-1, 145-150 87.2 72.0 7.63 3.25 36.0 10.74 477. 1.78 76. 564. 4.60 0. 1297. 27.52 10.8 53.5 13X-3, 145-150 120.0 60.0 7.75 3.45 36.0 9.48 437. 1.73 82. 568. 4.60 0. 1176. 25.56 11.3 53.1

Hole 869B

10R-1, 145-150 218.7 16.0 7.58 0.70 35.5 2.96 409. 0.24 228. 558. 0.84 17. 371. 20.79 63.3 20.3 11R-2, 145-150 229.9 28.0 7.89 0.34 36.0 2.39 426. 0.35 291. 565. 1.20 31. 247. 21.36 63.5 18.3 13R-1, 145-150 247.7 33.0 6.96 0.79 35.5 1.80 386. 0.27 276. 563. 1.60 28. 202. 19.15 62.8 17.5 17R-2, 0-5 285.8 4.0 35.0 2.24 430. 273. 560. 70. 20.84 20R-2, 145-150 316.8 25.0 8.19 0.58 36.5 1.71 431. 0.24 285. 547. 1.20 42. 143. 21.34 72.3 14.3 23R-1, 145-150 344.3 26.0 8.22 0.99 36.5 1.81 447. 0.23 272. 567. 1.20 38. 158. 23.63 70.4 15.3 31R-1, 145-150 421.6 5.5 36.5 1.86 414. 0.17 291. 570. 1.97 60. 659. 20.23 95.1 6.1 59R-1, 146-150 691.5 4.0 41.0 0.65 222. 120. 591. 0.69 48. 167. 12.55 190.6 4.4 65R-2, 145-150 750.9 15.0 39.0 0.50 208. 244. 561. 0.69 45. 257. 17.03 186.9 4.6 69R-1,27-32 788.0 7.5 39.0 0.51 246. 251. 571. 0.69 24. 228. 17.54 173.9 7.2

Alkal. = alkalinity; Salin. = salinity. Core designations include the core, drill type (H = hydraulic pistion corer, X = extended core barrel, R = rotary) and section number; water; water yield in the analyzed samples. SITE 869

The changes in pore-water concentration in the measured cations section, this chapter). The upper 32.5 mbsf is characterized by high- have been interpreted as reflecting diagenetic changes within the amplitude variations that range from 23.6% to 93.4% CaCO3, with a volcaniclastic sediments. Calcium and strontium are released from general upward decrease. The brown radiolarian ooze shows low-to- feldspars of the volcaniclastics, whereas magnesium, potassium, so- moderate carbonate content (between 23.6% and 53.7%), whereas dium, and rubidium are incorporated in the alteration products of the light-beige nannofossil ooze indicates higher values. The transition volcaniclastic sediments and, thus, are reduced in the pore water. The between beige and brown ooze is well documented. For example, a increase in salinity that was observed in the three lowest samples progressive upward decrease of carbonate content from light-beige results from an increase in calcium that more than compensates for ooze to overlying beige and brown radiolarian ooze was established decreases in the concentration of other cations (Table 3; Fig. 38). from the data of Core 143-869A-2H (Table 5). The redeposited white level occurring in Interval 143-869A-4H-3, 77-78 cm (see "Litho- Silica stratigraphy" section, this chapter) defines the base of the first part. The second part (Sections 143-869A-4H-3 to -9H-2), corresponding Silica concentrations range between 143 and 1297 µM (Table 3). to Subunit IB, shows relatively constant, high calcium carbonate The silica content of the pore water in general, and especially in contents, with values everywhere exceeding 91%. The third part Section 143-869B-13X-3, reflects the high biogenic silica concentra- (Section 143-869A-9H-4toCore 143-869A-15X) is characterized by tions in the radiolarian oozes of Hole 869A. an upward increase of calcium carbonate, with short-term high- amplitude variations. The CaCO3 contents fluctuate between 6.7% Ammonium, Sulfate, and Phosphate and 73.2%, which corresponds to the chert and claystone alternations The ammonium content varies between 0 and 70 µM, but all of of lithologic Unit II. the samples in Hole 869 A contained little (<22 µM) or no ammonium, In Hole 869B, 163 samples were analyzed for IC (Table 6). The whereas the samples from Hole 869B indicate a slight trend toward brown cherts occurring in Cores 143-869B-2R to -9R, and correspond- increasing concentration with depth (Fig. 39). The sulfate values ing to lithologic Unit II have very low calcium carbonate content decrease with depth (from 27.4 mM at the top of Hole 869A to (<1%), except for a white siliceous chalk (Sample 143-869B-4R-1, 12.55 mM in Section 143-869B-59R-1, Fig. 39), indicating a progres- 46^7 cm) that contains 76.6% CaCO3 (Fig. 41). Between 207.7 and sive increase in the amount of sulfate reduction. The increases in 458.8 mbsf (lithologic Subunits IIIA and IIIB), the carbonate record ammonium and decreases in sulfate concentrations in Holes 869 A and shows high-amplitude variations from 0.2% to 83.3%. The volcani- 869B presumably are associated with organic-matter decomposition. clastic sandstones and radiolarian claystones present lower values, Phosphate values are near the detection limit (~ 1 µM) of the whereas nannofossil-rich claystone and mudstone levels show high analytical method (see "Explanatory Notes" chapter, this volume), values. The thin Subunit IIIC is characterized by a sharp decrease of with a maximum concentration of 4.6 µM in Sections 143-869A- calcium carbonate content to values below 16.2%. The redeposited 10X-1 and -13X-3. No increases in phosphate concentrations were volcaniclastic facies forming lithologic Subunits HID to IIIF contain observed in the volcaniclastic sediments. little calcium carbonate (<5%), except for a few horizons that occur in Cores 143-869B-48R, -50R, -51R, and -55R, where fine sandy facies contain between 13% and 60% CaCO3. It seems that within the tur- ORGANIC GEOCHEMISTRY bidite beds the coarser layers indicate lower calcium carbonate contents At Site 869, in addition to safety monitoring for hydrocarbon than the interlayers of fine sandstone and claystone beds. Subunit IIIG, gases, 234 samples were used to determine carbonate content with the where calcareous claystone with radiolarians and pale green mudstone Coulometrics carbon dioxide coulometer. Total nitrogen, sulfur, and are present again, shows a slight increase of carbonate (Fig. 41). carbon contents were measured by means of an NA 1500 Carlo Erba NCS analyzer. The procedures used for these analyses are outlined in Organic Carbon Contents the "Explanatory Notes" chapter (this volume). Total organic carbon (TOC) values were calculated by difference Volatile Hydrocarbons between total carbon, determined with the NCS analyzer, and IC. The results of 234 analyses from Holes 869A and 869B are reported in As part of the shipboard safety and pollution monitoring program, Tables 5 and 6, respectively. Total nitrogen and sulfur concentrations the hydrocarbon gases were measured in the sediments at Site 869, commonly are below the detection threshold of the NCS analyzer using the headspace technique and the Carle gas chromatograph to (Table 5). Thus, TOC/N and TOC/S ratios tend thus to be highly determine C,-C3 concentrations. The results of 39 headspace analyses variable; the highest ratios are generally recorded in samples that are are reported in Table 4. Only very low levels of volatile hydrocarbon low in both nitrogen and sulfur. were detected. Methane concentrations range from 2 to 5 ppm, In Hole 869A, the total organic carbon contents are very low. TOC whereas traces of ethane are noted, but are below the concentration fluctuates from 0% to 0.67%, with a mean value of 0.15% (Fig. 42). threshold of the integrator. Compared with a laboratory background In Hole 869B, the organic contents measured are low throughout of 2 ppm, the concentrations in the sediment are minor. The low the sampled interval. TOC fluctuates from 0% to 0.76% (Fig. 43). The overall content of methane in the sediments suggests that either the lowest TOC contents can be found in the chert facies of lithologic biogenic methane usually produced during microbial degradation of Unit II and in the coarse volcaniclastic facies of lithologic Sub- organic matter migrated out of the sedimentary column, or that units HID to IIIF. These values are somewhat higher in fine siltstone conditions were not favorable enough to sustain methanogenesis. and claystone levels of Unit III, but still remain below 0.7% TOC. Surprisingly, some beige claystones and volcaniclastic sandstones Inorganic Carbon contain about 0.5% TOC. It is not yet clear if these values are geochemically significant or if they are at least partly the result of a In Hole 869A, 71 samples were analyzed for inorganic carbon systematic error in the analytical procedure (e.g., by acid-resistant (IC). The calcium carbonate content is variable in relation to the carbonate which could yield too high a difference between total primary nature of the lithologic facies (Table 5). According to the carbon and IC). calcium carbonate record, the sedimentary sequence in Hole 869A Twelve samples were analyzed using the Geofina hydrocarbon can be divided into three parts (Fig. 40) that correspond well to meter (Table 7). Only four samples show values that can be inter- lithologic Subunits IA and IB and Unit II (see "Lithostratigraphy" preted. In accordance with their low organic carbon content, their

331 SITE 869

Alkalinity Salinity (‰) CI~(mM) 9 0 1 2 34.5 35.5 36.5 400 440 480 520 560 600 1 1 1 1 1 01 o I u 0 o o o o o o 1 1 c

o O - o o o 0 -

o O 0 - o o

500 1 1 1 1 1 1 K+(mM) Rb+(µM) Na+(mM) 4 6 8 10 120 0.5 1 1.5 2 200 300 400 500 I 1 1 U II 1

o°° 0 o o o o

o 0

_ o o 1 1 1 Ol 1 1 1 1 Ca+2(mM) Mg+2(mM) Sr+2(µM) 50 100 150 200 0 10 20 30 40 50 60 50 100 150 200 250 300 0' 1 1 1 1 1 U U | | | 1 o o o o o o 100 _o o _ o o o o 200 §

600

700 o_ _o o o o o 800 I I I O O I I | I | I I I C

Figure 38. The pH, alkalinity, salinity, and concentrations of chloride, potassium, rubidium, sodium, calcium, magnesium, and strontium as a function of depth in Holes 869A and 869B. hydrocarbon potential is very low. S, signals are extremely low, and PHYSICAL PROPERTIES S2 values remain below 0.24 mg hydrocarbon/g dry sediment. Fur- thermore, Tmax parameters were difficult to calculate on the basis of Introduction very flat S2 peaks. Tmax values (ranging from 345 to 454) indicate that no clear maximum is discernible. The approximate HI values are very Site 869 objectives were to drill the deep-apron location Syl-3 to low (<58 mg hydrocarbons/g TOC) and indicate that the organic recover sediments having a possible provenance from Wodejebato matter may consist of so-called "dead carbon" or type IV organic Guyot and Pikinni Atoll. The objectives of the physical-property meas- matter (i.e., organic matter that has been completely oxidized and urement program were (1) to measure the standard shipboard physical deprived of its hydrogen content). properties, to analyze P-wave velocities in unlithified to fully lithified

332 SITE 869

+4 NH4(µM) PO4(mM) Si (µM) S04 (mM) 0 20 40 60 80 0 1 2 3 4 5 0 400 800 1200 12 16 20 24 28 0 JI r i i o o 100

200

% 300 XI E ~ 400

Q 500

600

700

800 I I O I I I I I IP I I I

Figure 39. Concentrations of ammonium, phosphate, silica, and sulfate as a function of depth in Holes 869A and 869B. sediments, to measure thermal conductivity, and to collect GRAPE- velocity from the DSV, bulk density (discrete measurements), and density and P-wave velocity data from the multisensor track (MST); percentage of recovery. Bulk density and sonic velocities from physi- and (2) to identify physical-property units for correlation with down- cal-properties sediments have been compared with log measurements hole logs (sonic velocity, gamma-ray, and density), lithology, and with and lithologic units in Figure 47. discrete measurements of P-wave velocity and index properties. Sediments recovered at Site 869 comprise unlithified to semi- Physical Property Units lithified nannofossil and radiolarian ooze (0-207.7 mbsf) and vol- canic claystone, sandstone, and breccia, alternating with intervals of Five major physical-property units were defined for Site 869 on nannofossil to radiolarian-rich claystone and chalk (207.7- the bases of significant downhole trends in index properties, P-wave 796.2 mbsf). measurements, and in one instance, anisotropy of sonic velocity. Only The unlithified to semilithified sediments, drilled with the APC a few boundaries have been associated with lithologic features. De- and XCB, showed variable indications of coring disturbance. Never- pending on recovery and sample-spacing, most boundaries for physi- theless, they were run through the MST for GRAPE density and cal property (PP) units have been arbitrarily placed midway between P-wave velocity and measured for thermal conductivity. In addition, discrete samples (see Fig. 46). In the following section, unless men- measurements for P-wave velocity were performed using the digital tioned otherwise, data presented for sonic velocity are those measured sound velocimeter (DSV) down to a depth of 226.9 mbsf in Hole 869B in the vertical direction from cubes. Similarly, data about index and then cored with the RCB. At this depth, sediments were too dense properties were those measured from cubes. and too physically disturbed to use the DSV longer, so discrete samples were collected from deeper intervals for P-wave velocity Physical Property Unit 1 (Hole 869A: 0-166.5 mbsf; Hole 869B: measurements in both longitudinal and transverse directions with the Hamilton Frame apparatus. For each pair of horizontal and vertical 149.6-210 mbsf) velocity measurements, the anisotropy was calculated. Discrete meas- This unit consists of unlithified to semilithified clayey nannofossil urements of index properties in Hole 869A: bulk density, porosity, to radiolarian ooze with, near the bottom, chert intervals. In the upper water content (expressed as percentage of dry weight), and grain part, between 0 and 80 mbsf, recovery was near 100%. From about density seemed to be in good agreement with the GRAPE-density 80 to 145 mbsf, recovery was approximately 60%, but between 145 logs. In Hole 869B, index properties were measured using the cubes and 210 mbsf, recovery was only about 5%. Along with trends in collected for P-wave velocity measurements. No correction for salt physical properties, percentage of recovery was used to identify the content was made (see "Physical Properties" section, "Site 866" boundaries of the PP units. Sonic velocity shows a gradual downhole chapter, this volume). increase to about 145 mbsf. Between 145 and 210 mbsf, recovery In general, recovery was good and permitted correlations among decreases abruptly, and high-velocity lithologies were recovered. the various tools measuring density (GRAPE-density and density from Bulk density increases gradually down to about 75 mbsf, decreases discrete measurements of beaker samples and cubes) and P-wave downhole between 75 and 100 mbsf, and remains steady down to velocity (P-wave logger, DSV, and discrete measurements). Further- about 150 mbsf. Between 150 and 225 mbsf, preferentially high-den- more, correlations could be made among lithology, physical-property sity lithologies were recovered. units, and well logs. Data for Holes 869A and 869B are presented in Tables 8, 9, 10, Physical Property Subunit la (Hole 869A: 0-80 mbsf) and 11, giving the index properties, discrete sonic velocity measure- ments, velocity measurements performed with the DSV and thermal The lower boundary of this subunit, consisting of unlithified conductivity readings, respectively, as a function of depth. Figure 44 clayey nannofossil to radiolarian ooze, has been defined by the abrupt presents the depth distribution of index properties, GRAPE density, changes in recovery and bulk density (measured from discrete sam- and sonic velocity from discrete measurements for both Holes 869A ples) at 80 mbsf. However, sonic velocity shows a gradual increase and 869B. Figure 45 shows the depth distribution of P-wave velocity over this range (both from discrete samples as well as from the DSV) from the MST (P-wave logger) and velocity measured by the DSV, from 1.45 to 1.55 km/s. Overall, bulk density increases downcore discrete bulk-density measurements, and GRAPE density for from 1.2 to 1.8 g/cm3, porosity shows scattered values in the first Hole 869A. Figure 46 shows the depth distribution of sonic velocity 50 mbsf, followed by steady values of 55% to 60%, and water content and anisotropy of sonic velocity from discrete measurements and (% dry weight) decreases from 60% to 40%.

333 SITE 869

Table 4. Hydrocarbon gas data for Site 869. than 5%. Discrete measurements of index properties and sonic veloc- ity thus are not representative for in-situ values. Bulk density ranges 3 Core, section, Depth Sample c, from 1.43 to 2.54 g/cm , water content (% dry weight) ranges from interval (cm) (mbsf) type11 (ppm) 0.94% to 110.05%, and porosity varies between 2.28% and 74.96%. Sonic velocity from cubes ranges from 2.07 to 4.91 km/s. The upper Hole 869A and lower boundaries of this subunit were selected at the first and last 1H-5, 142-143 7.42 HS 3 occurrences of high velocities caused by the presence of chert intervals. 3H-4, 0-3 23.70 HS 3 4H-6, 0-3 36.20 HS 4 5H-6, 0-3 45.70 HS 3 Physical Property Unit 2 (Hole 869B: 210-377 mbsf) 6H-6, 0-3 55.20 HS 3 Physical property Unit 2 had variable recovery, with values rang- 7H-6, 0-3 63.32 HS 3 8H-4, 0-3 69.75 HS 2 ing between 5% and 50%, that reflect the alternation of semi-indu- 9H-2, 0-3 77.70 HS 3 rated nannofossil claystone and calcareous layers and volcaniclastic 10X-2, 0-3 87.20 HS 2 sand- to siltstone. Consequently, physical properties are variable. HX-3,0-3 98.50 HS 3 Bulk density values range from 1.47 to 2.58 g/cm3, with a mean of 12X-3, 0-3 108.50 HS 4 3 I3X-3, 142-145 119.92 HS 3 1.98 g/cm . Water content ranges from 7.46% to 89.36%, with a mean 14X-4, 147-150 131.47 HS 3 of 4226%, and porosity varies between 17.94% and 71.81%, with an 15X-6. 69-71 143.69 HS 2 average of 50.09%. P-wave velocity ranges from 1.05 to 2.67 km/s, with an average of 1.95 km/s. The slightly lower values of bulk den- Hole 869B sity and velocity correspond to the less-indurated and more-porous HR-2. 142-145 229.82 HS 2 nannofossil claystone and calcareous layers. The lower boundary of I3R-1, 142-145 247.62 HS 3 PP Unit 2 corresponds with an abrupt downcore increase of sonic ve- 15R-4, 147-150 271.37 HS 3 locity at approximately 377 mbsf. 16R-1,0-3 275.10 HS 3 17R-2, 2-5 285.85 HS 3 18R-CC, 0-3 294.40 HS 3 Physical Property Unit 3 (Hole 869B: 377-534 mbsf) 19R-3, 84-85 307.94 HS 3 20R-2, 142-145 316.72 HS 3 Physical properties in Unit 3 show a decrease downcore in bulk 21R-1, 106-107 324.56 HS 3 density and sonic velocity in the interval from 377 to 425 mbsf 22R-1, 147-150 334.57 HS 3 (Subunit 3a), followed by a gradual increase downcore in the lower 23R-1, 142-145 344.22 HS 3 25R-3, 88-89 366.08 HS 3 interval from 425 down to 534 mbsf (Subunit 3b). Sediments consist 26R-1, 149-150 373.29 HS 3 of radiolarian clay- to siltstone and, near the base of Subunit 3b, vol- 27R-1,40-41 381.90 HS 3 caniclastic breccias. An overall increase in recovery occurs downcore 28R-CC. 18-19 391.28 HS 3 from about 5% to 50%, corresponding to the gradual increase down- 29R-CC.8-9 400.88 HS 3 32R-1.0-3 429.80 HS 3 core in volume of volcaniclastics. 35R-1.37-38 459.17 HS 3 36R-1, 144-145 469.84 HS 4 Physical Property Subunit 3a (Hole 869B: 377-425 mbsf) 37R-CC, 0-3 478.10 HS 4 38R-3, 140-142 491.24 HS 3 Sediments in this PP subunit are predominantly radiolarian clay- 39R-CC, 10-11 500.22 HS 3 stone and thin layers of volcaniclastic silt to sand. Physical properties, 49R-CC, 0-3 593.50 HS 5 57R-4, 0-3 675.20 HS 4 bulk density, and sonic velocity near the top of the unit are higher and 65R-2, 144-145 750.84 HS 3 more constant than in the overlying PP Unit 2. Bulk density ranges from 1.87 to 2.14 g/cm3, with an average of 2.02 g/cm3, water content d HS = headspace vial. ranges from 12.31% to 32.47%, with a mean value of 19.61%, and porosity ranges from 22.80% to 47.00%, with a mean value of 32.09%. Physical Property Subunit lb (Hole 869A: 80-145 mbsf) Sonic velocity shows a gradual decrease downcore from about 3 to 2 km/s near the lower boundary of this unit. This boundary with under- Subunit lb mainly consists of nannofossil ooze and, downcore, has lying PP Subunit 3b marks a sharp break in density and sonic velocity. relatively constant index properties and sonic velocity. The upper boundary was defined on the bases of an abrupt shift in bulk density Physical Property Subunit 3b (Hole 869B: 425-534 mbsf) (discrete samples), from 1.70 to 1.55 g/cm3 (downcore), and recovery, from 100% to 30%. The lower boundary was selected where recovery The upper part of PP Subunit 3b consists of radiolarian claystone decreased to about 5% to 10% and the chert intervals were first cored. and siltstone, as in overlying Subunit 3a, and has moderately low On average, bulk density has values that range from 1.23 to 2.15 g/cm3, values of bulk density and sonic velocity that range from about 1.8 to water content ranges from 1.85% to 222.5% (dry weight), and porosity 1.9 g/cm3 and from 2 to 2.5 km/s, respectively. The lower part of ranges from 3.91% to 90.3%. Sonic velocity, measured by the DSV, is Subunit 3b consists of a thick interval of volcaniclastic breccia relatively constant and varies between 1.50 and 1.55 km/s. One core (lithologic Unit HID) and shows an increase downcore in density and (Section 143-869A-10X-CC) contained a chert pebble with a sonic velocity up to 2.1 g/cm3 and about 4 km/s, respectively. The lower velocity (measured on the Hamilton Frame) of 3.95 km/s. Overall, boundary of PP Subunit 3b is sharp and corresponds to a rapid physical properties in this unit were constant, and it had lower densities decrease in sonic velocity in underlying Unit 4. In addition, this and velocities than the overlying PP Subunit 1 a. boundary correlates with the change from lithologic Subunits HID to HIE. In general, values of bulk density range from 1.81 to 2.28 g/cm3, 3 Physical Property Subunit lc (Hole 869A: 145-166.5 mbsf; with an average of 2.04 g/cm , water content ranges from 9.39% to 34.85%, with a mean of 22.17%, and porosity varies between 19.60% Hole 869B: 149.6-210 mbsf) and 48.01 %, with an average of 35.89%. f-wave velocity ranges from Physical property measurements in Subunit lc were limited to 1.88 to 4.02 km/s, with a mean of 2.74 km/s. The gradual increase well-indurated chert intervals, as the softer clayey nannofossil to downcore of sonic velocity and, in part, bulk density (in the lower radiolarian oozes were washed out. Recovery was on average lower part of Subunit 3b) about 380 down to 534 mbsf, corresponds to a SITE 869

Table 5. Concentrations of total, inorganic, and organic carbon and of total nitrogen and sulfur in sediments from Hole 869A.

Core, section, Depth Sample TC IC TOC CaCO, N s interval (cm) (mbsf) type" (%) (%) (%) (%) (%) (%) TOC/N TOC/S Lithology 143-869A- 1H-1, 81-82 0.81 CARB 8.72 8.61 0.11 71.7 0.01 0.23 11.0 0.5 Light-brown ooze 1H-5, 77-78 6.77 CARB 2.94 2.83 0.11 23.6 0.01 0.00 11.0 Brown ooze 1H-5, 145-150 7.45 IWSC 11.14 11.10 0.04 92.5 0.05 0.00 0.8 Light-brown ooze 2H-1,39—40 10.09 CARB 7.78 7.75 0.03 64.6 0.01 0.00 3.0 Light-brown ooze 2H-1,60-61 10.30 CARB 6.63 6.41 0.22 53.4 0.00 0.06 3.6 Light-brown ooze 2H-1,80-81 10.50 CARB 4.06 3.86 0.20 32.2 0.02 0.22 10.0 0.9 Brown ooze 2H-1, 100-101 10.70 CARB 7.51 7.36 0.15 61.3 0.01 0.10 15.0 1.5 Light-brown siliceous ooze 2H-2, 30-31 11.50 CARB 9.24 9.23 0.01 76.9 0.01 0.10 1.0 0.1 Light-brown ooze 2H-2, 50-51 11.70 CARB 7.05 6.89 0.16 57.4 0.01 0.18 16.0 0.9 Light-brown ooze 2H-2, 60-61 11.80 CARB 8.83 8.41 0.42 70.1 0.08 0.12 5.2 3.5 Light-brown ooze 2H-2, 65-66 11.85 CARB 9.08 9.04 0.04 75.3 0.03 0.08 1.0 0.5 Light-brown ooze 2H-2, 70-71 11.90 CARB 11.04 10.92 0.12 91.0 0.00 0.00 White ooze 2H-2, 75-76 11.95 CARB 10.97 10.93 0.04 91.0 0.00 0.04 1.0 White ooze 2H-2, 85-86 12.05 CARB 11.02 11.00 0.02 91.6 0.01 0.00 2.0 White ooze 2H-2, 100-101 12.20 CARB 11.09 11.07 0.02 92.2 0.01 0.00 2.0 White ooze 2H-5, 1-2 15.71 CARB 11.09 10.86 0.23 90.5 0.01 0.00 23.0 Light-brown ooze 2H-5, 20-21 15.90 CARB 11.22 11.21 0.01 93.4 0.01 0.00 1.0 White ooze 2H-5, 40^11 16.10 CARB 10.88 10.87 0.01 90.5 0.00 0.00 Light-brown ooze 2H-5, 59-60 16.29 CARB 10.99 10.81 0.18 90.0 0.00 0.00 Light-brown ooze 2H-5, 79-80 16.49 CARB 10.95 10.90 0.05 90.8 0.00 0.00 White ooze 2H-5, 99-100 16.69 CARB 11.24 11.13 0.11 92.7 0.00 0.01 11.0 White ooze 3H-1,69-70 19.89 CARB 10.34 10.01 0.33 83.4 0.07 0.00 4.7 Light-brown ooze 3H-3, 82-83 23.02 CARB 5.65 5.60 0.05 46.6 0.00 0.12 0.4 Brown ooze 3H-5, 73-74 25.93 CARB 10.22 9.96 0.26 83.0 0.00 0.00 White ooze 3H-7, 30-31 28.50 CARB 9.12 9.00 0.12 75.0 0.00 0.00 Light-brown ooze 4H-1,76-77 29.46 CARB 9.82 9.74 0.08 81.1 0.01 0.01 8.0 8.0 Light-brown ooze 4H-3, 66-67 32.36 CARB 10.43 10.07 0.36 83.9 0.00 0.00 Light-brown ooze 4H-3, 71-72 32.41 CARB 8.13 8.01 0.12 66.7 0.00 0.05 2.4 Brown ooze 4H-3, 77-78 32.47 CARB 6.86 6.45 0.41 53.7 0.00 0.09 4.5 Brown ooze 4H-3, 81-82 32.51 CARB 11.53 11.34 0.19 94.5 0.01 0.00 19.0 White turbiditic layer 4H-3, 85-86 32.55 CARB 11.52 11.40 0.12 95.0 0.00 0.00 White ooze 4H-3, 92-93 32.62 CARB 11.46 11.33 0.13 94.4 0.00 0.00 Light-brown ooze 4H-5, 145-150 36.15 IWSC 11.92 11.57 0.35 96.4 0.03 0.16 11.0 2.2 Light-brown ooze 4H-6, 59-60 36.79 CARB 11.29 11.18 0.11 93.1 0.00 0.00 Light-brown ooze 5H-1, 101-102 39.21 CARB 11.44 11.24 0.20 93.6 0.00 0.00 Light yellowish ooze 5H-3, 25-26 41.45 CARB 11.31 11.16 0.15 93.0 0.01 0.12 15.0 1.2 Light yellowish ooze 5H-4, 78-79 43.48 CARB 11.65 11.34 0.31 94.5 0.01 0.00 31.0 White ooze 5H-6, 80-81 46.50 CARB 10.96 10.95 0.01 91.2 0.03 0.00 0.3 White ooze 6H-2, 76-77 49.96 CARB 11.31 11.10 0.21 92.5 0.00 0.00 White ooze 6H-4, 75-76 52.95 CARB 11.43 11.25 0.18 93.7 0.02 0.00 9.0 White ooze 6H-6, 75-76 55.95 CARB 11.26 11.17 0.09 93.0 0.00 0.00 Light yellowish ooze 7H-2, 39^0 57.71 CARB 11.47 11.32 0.15 94.3 0.01 0.00 15.0 White ooze 7H-2, 75-76 58.07 CARB 11.34 11.26 0.08 93.8 0.00 0.00 White ooze 7H-5, 145-150 63.27 IWSC 11.80 11.58 0.22 96.5 0.05 0.13 4.4 1.7 White ooze 8H-3, 77-78 69.02 CARB 11.65 11.58 0.07 96.5 0.05 0.00 1.0 White ooze 8H-6, 86-87 73.61 CARB 11.43 11.20 0.23 93.3 0.08 0.00 2.9 White ooze 8H-8, 71-72 76.46 CARB 11.47 11.51 95.9 0.07 0.00 White ooze 9H-2, 78-80 78.48 CARB 12.11 11.70 0.41 97.5 0.07 0.00 5.8 White ooze 9H-4, 79-81 81.49 CARB 7.98 8.00 0.00 66.6 0.07 0.24 0.0 0.0 Light-beige ooze 9H-6, 77-79 84.47 CARB 8.68 8.61 0.07 71.7 0.09 0.25 0.8 0.3 Light-beige ooze 1 OX-1,73-74 86.43 CARB 8.06 7.39 0.67 61.6 0.10 0.00 6.7 Beige ooze 10X-1, 145-150 87.15 IWSC 6.20 5.98 0.22 49.8 0.07 0.24 3.1 0.9 Brown ooze 10X-2, 69-70 87.89 CARB 8.23 8.20 0.03 68.3 0.09 0.23 0.3 0.1 Light-beige ooze 10X-CC, 5-6 88.34 CARB 2.59 2.41 0.18 20.1 0.09 0.00 2.0 Siliceous chalk 11X-2, 82-83 97.82 CARB 7.33 6.91 0.42 57.6 0.08 0.30 5.2 1.4 White ooze 11X-4, 36-37 100.36 CARB 5.92 5.45 0.47 45.4 0.07 0.00 6.7 White ooze 12X-1,62-63 106.12 CARB 8.89 8.79 0.10 73.2 0.08 0.25 1.2 0.4 White ooze 12X-4, 66-67 110.66 CARB 0.84 0.80 0.04 6.7 0.08 0.33 0.5 0.1 White ooze 12X-5, 104-105 112.54 CARB 8.65 8.64 0.01 72.0 0.12 0.25 0.1 0.0 White ooze 12X-5, 116-117 112.66 CARB 1.19 1.04 0.15 8.7 0.10 0.31 1.5 0.5 Light-beige ooze 13X-2, 23-24 117.23 CARB 1.14 0.88 0.26 7.3 0.17 0.40 1.5 0.7 Light-beige ooze 13X-3, 145-150 119.95 IWSC 0.49 0.35 0.14 2.9 0.06 0.00 2.3 Light-brown ooze 13X-4, 50-51 120.50 CARB 0.13 0.03 0.10 0.2 0.09 0.00 1.1 Light-beige ooze 13X-CC.4-5 121.66 CARB 8.80 8.59 0.21 71.6 0.08 0.25 2.6 0.8 Light-beige ooze I4X-1,86-87 126.36 CARB 5.94 6.03 50.2 0.85 0.00 Light-beige ooze 14X-3, 38-39 128.88 CARB 2.00 1.98 0.02 16.5 0.20 1.04 0.1 0.0 Light-beige ooze 14X-5, 46^7 131.96 CARB 0.14 0.04 0.10 0.3 0.10 0.00 1.0 Beige ooze 15X-2, 69-70 137.69 CARB 0.12 0.04 0.08 0.3 0.08 0.31 1.0 0.3 Light-beige ooze 15X-2, 114-115 138.14 CARB 0.54 0.49 0.05 4.1 0.10 0.26 0.5 0.2 White ooze 15X-4, 10-11 140.10 CARB 2.47 2.51 20.9 0.06 0.23 White ooze 15X-6, 32-33 143.32 CARB 2.28 2.25 0.03 18.7 0.08 0.25 0.4 0.1 White ooze

1 Sample type: CARB = carbonate; IWSC = interstitial-water squeeze cake. SITE 869

16.04% and 42.79%, averaging 29.66%. Rapid fluctuations in sonic CaCO3 (%) Lith. 0 20 40 60 80 units velocity are suggested to correlate with changes in sediment fabric and mineralogy within the volcaniclastics. The presence of a zeolite cement instead of clay in the volcaniclastics and of elevated carbonate percentages in the clayey nannofossil and radiolarian oozes tends to increase the relative sonic velocity. The lower boundary of PP Sub- unit 5a exhibits a gradual decrease in the variability of sonic velocity and, in addition, a subtle change in anisotropy of velocity. The general decrease downcore in anisotropy in Subunit 5a reverses into an increase downcore in Subunit 5b. This boundary has no correlative lithologic contact.

Physical Property Subunit 5b (Hole 869B: 720-796.2 mbsf) Physical properties in PP Subunit 5b are relatively constant down- core: bulk density ranges from 1.90 to 2.36 g/cm3, with an average of 2.60 g/cm3, water content ranges from 3.58% to 30.69%, with an average of 20.68%, and porosity varies between 7.46% and 44.61 %, with a mean of 34.14%. Sonic velocity has values that range from 2.44 to 4.36 km/s, with an average of 2.92 km/s. Sediments consist primarily of volcaniclastic siltstone to sandstone with nannofossil and 150 radiolarian claystone and, near the bottom (from about 780 mbsf downward), an increase in carbonate content (see "Organic Geochem- Figure 40. Depth distribution of calcium carbonate in Hole 869A. istry" section, this chapter).

change from more muddy, fine-grained volcaniclastics to predomi- Discussion nantly coarse-grained, locally pebbly, cemented volcaniclastics (see "Lithostratigraphy" section, this chapter). Recovery at Site 869 was high, nearly 100%, in the unlithified to semilithified upper part (0-145 mbsf), moderate, 5% to 45%, in the Physical Property Unit 4 (Hole 869B: 534-639 mbsf) section containing well-layered volcaniclastics and chalks from about 145 to about 600 mbsf, and high again in the lower portion, on average The top of PP Unit 4 is the well-defined lower boundary of a thick more than 60%, from about 600 down to 796.2 mbsf, that contains succession, about 55 m thick, that consists of coarse-grained volcani- predominantly massive volcaniclastic layers. Therefore, these data clastic breccias then changes downcore into alternating radiolarian should reflect, with the exception of the poorly recovered section of claystone, nannofossil chalk, and volcaniclastic siltstone and sand- PP Subunit lc, the lithologic succession at Site 869. Physical proper- stone. Mass physical properties within Unit 4 are relatively constant ties (see Fig. 46) indicate a general subdivision into three major 3 downcore; bulk density varies between 1.96 and 2.45 g/cm , with an intervals: (1) an uppermost interval, 0 down to 210 mbsf, of unlithified 3 average of 2.12 g/cm , water content ranges from 5.49% to 28.45%, to semilithified nannofossil to radiolarian ooze having low densities with an average of 19.67, and porosity ranges from 12.74% to and low velocities, including a chert-rich interval having low recov- 43.43%, with a mean value of 34.01%. Sonic velocity ranges from ery; (2) an intermediate interval, 210 to 377 mbsf, characterized by 2.14 and 4.73 km/s, with an average of 2.75 km/s. The lower boundary highly variable bulk density and, to a minor extent, sonic velocity of PP Unit 4 shows a well-defined and abrupt downcore increase in consisting of alternating, thin-layered volcaniclastics and semi-indu- the range of sonic velocity and correlates with the change from rated nannofossil claystone; and (3) a lowermost interval, 377 down lithologic Subunit HIE to the underlying lithologic Subunit IIIF to 796.2 mbsf, of well-layered to massive volcaniclastics with minor (depth of boundaries are 639 and 653.3 mbsf, respectively). From nannofossil to radiolarian chalk and claystone, characterized by well- about 600 mbsf downward, overall recovery increases dramatically defined trends in bulk density and sonic velocity. from less than 5% to 70%. No apparent correlation is present between Boundaries between PP units generally correspond to changes in this change in recovery and physical properties and/or lithology. lithology, as indicated by downhole logs where recovery was sparse, or to major changes in character of gravity deposits within these Physical Property Unit 5 (Hole 869B: 639-796.2 mbsf) lithologic units (Fig. 47). Few boundaries have no correlation with lithologic units, (e.g., the lower boundary of PP Subunit 5a). This may On average, sonic velocity values in PP Unit 5 are slightly higher also be related to a zone of low recovery. We postulate that higher and more varied than those in the overlying PP Unit 4. The upper part frequency variations within the lower PP units (Units 3, 4, and 5) are of PP Unit 5, 639 to 720 mbsf (Subunit 5a), shows a high variance in related to the alternation of lithologies of different fabric and miner- sonic velocity, with values ranging from about 2.1 to more than 5 km/s. alogy. Within volcaniclastic successions, in general, muddy textures The lower part of PP Unit 5, 720 to 796.2 mbsf (Subunit 5b), has more have lower velocity and bulk density than textures devoid of mud and constant values of sonic velocity. The sediments constituting PP Unit cemented by zeolite. Similarly, higher carbonate concentrations in 5 are predominantly volcaniclastic sandstone and siltstone alternating pelagic sediments tend to increase the sonic velocity and bulk density. with minor amounts of nannofossil- and radiolarian-rich layers. Major changes in velocity and density are correlated with boundaries between lithologic subunits that consist of a base of coarse, gravelly, Physical Property Subunit 5a (Hole 869B: 639-720 mbsf) volcaniclastic debris flows with finer-grained volcaniclastics, alter- Although bulk density shows little downcore variation in Subunit nating with pelagic sediments toward the top (see also "Lithostra- 5a (ranging from 1.89 to 2.25 g/cm3, with an average of 2.08 g/cm3), tigraphy" section, this chapter). The lithologic contacts at 536.1 and sonic velocity is highly variable and ranges from 2.38 up to 5.50 km/s, 653.3 mbsf (the boundaries between lithologic Subunits IIID/IIIE and with an average of 3.29 km/s. Water content ranges from 8.70% to IIIE/IIIF, respectively) have corresponding signatures in sonic veloc- 28.69%, with an average of 17.01%, and porosity varies between ity and, to a lesser extent, bulk density (the boundaries between PP SITE 869

Subunit 3b/Unit 4 and Unit 4/Subunit 5a, respectively). However, the Log Relationships resulting change in physical properties, downcore decrease or in- crease, is not the same for both transitions, which may be related to Velocity and resistivity correlate well throughout the entire logged degree of induration and/or fabric type. The slight change in anisot- interval at Site 869 (Fig. 48). The extremely high variability in both ropy of velocity at about 720 mbsf has no direct correlation with a resistivity and velocity indicates correspondingly high variability in lithologic change or has been obscured because of low recovery. This porosity. Increases in velocity and density with depth do not follow a may reflect a significant transition in clay mineralogy and therefore simple compaction profile, suggesting that diagenesis and grain-size clay fabric, or a change in compaction history. Both the trends in fluctuation affect porosity much more than does mechanical compac- anisotropy as well as the physical property features associated with tion. The most notable feature is that zones exist where the resistivity, the lithologic transitions over the boundaries between different vol- velocity and density decrease with increasing depth, contrary to the caniclastic gravity flows need further study. normal compaction profile (e.g., logging Unit 5, Figs. 48 and 49). Velocity and resistivity decrease gradually with depth from the top of DOWNHOLE MEASUREMENTS logging Subunit lb to the base of logging Unit 2. Below logging Unit 2, the base level of resistivity increases gradually, but superim- Introduction posed on this base level are the highly resistive peaks of the sand- Wireline measurements were conducted at Hole 869B, which pene- stones and breccias (Fig. 48). trated 796.2 m of calcareous oozes, cherts, and volcaniclastic turbidite Furthermore, resistivity, velocity, and density correlate moderately deposits at a basinal fan site southwest of Wodejebato Guyot and well with the gamma-ray log (SGR in Fig. 49), in that the gamma-ray Pikinni Atoll. Four tool strings were run during the logging program maxima correspond to velocity, resistivity, and density minima. Higher at Hole 869A, including the sonic-porosity-density-resistivity-gamma- clay-mineral concentration is evident by higher gamma-ray counts and ray-temperature, the geochemical tool string, the Japanese downhole porosity (clay minerals substantially increase the porosity of uncom- magnetometer, and the FMS temperature tool string. We positioned the pacted [<2 km overburden] sediments). The abundances of thorium bottom of the drill pipe at 89.0 mbsf, and good logs were obtained and potassium seen in Figure 50 account for most of the SGR signal within the open borehole between 89.0 and 778.5 mbsf for the geo- in the logged interval; the uranium signal increases near the end of the physical tool string. Bridges (i.e., formations causing reduced hole logged interval. The potassium log exhibits a variable style, with values sizes that were impassible for logging tools) controlled the logging in the range of 0% to 7% and with some peaks that correlate with low- strategy thereafter. Following several failed attempts to break through resistivity and velocity anomalies, the most notable of which is at the an obstruction at about 166.0 mbsf, the pipe was lowered to 238.4 mbsf base of logging Unit 4. for the FMS. The magnetometer was run from 724.2 to 234.8 mbsf. Figure 51 presents a strong correlation among the geochemical Because of time constraints the geochemical tool was run only from logs. Log values for potassium, aluminum, and silica (all abundant in 560.2 to 360.0 mbsf. the clay minerals illite and kaolinite) are positively correlated with each other. Iron values are somewhat correlated with values for these Reliability of Logs other elements, but in general, variations in iron values probably are related to the volcanic influx. Calcium values are uniformly zero for Logging data from Hole 869A cover the interval from the bottom the entire logged portion of Hole 869B. The porosity log in Figure 49 of the drill string (89.0 mbsf) to near the base of the hole at 778.5 mbsf, only moderately correlates with resistivity and velocity logs. and all are of generally high quality. Hole size is the most important control on accuracy of the logs in Hole 869A. Two caliper logs were Temperature obtained on two separate runs: the lithodensity tool caliper, and the four-arm caliper of the FMS. The two give generally similar results, The data recorded on both logging runs were not useful because except that the FMS caliper has a maximum opening of 16 in. the pressure transducer in the tool malfunctioned. (40.64 cm), and the lithodensity caliper measures to a maximum of 18 in. (45.7 cm). Broad swings in the hole size from about 650 to Downhole Three-component Magnetometer Log 700 mbsf are probably related to changes in circulation patterns during drilling. Very large hole diameters (>17 in. or 43.16 cm) over The magnetometer measured three components of the geomag- the intervals at 90.0-165.2, 263.4-333.6, 473.2-499.2, and 558.7- netic field within Hole 869B from 239 to 725 mbsf. Because the mag- 598.2 mbsf account for questionable FMS and density/porosity data netometer takes a measurement every 3 s, at the speed of 500 m/hr, from these zones. Most other logs do not require pad contact and the sampling interval was about 0.4 m. The horizontal and vertical therefore are less insensitive to the changes in borehole size. components of the magnetic field inside the hole were calculated from Some occurrence of both cycle skipping and noise interference the observed three components of the magnetic field. The orientation can be seen in the sonic-velocity logging data. The noise problems of the tool with respect to the present geomagnetic field also was are predominantly localized to specific depths, and we anticipate that determined from the magnetic field measured by the two orthogonal many of the problems with noise can be overcome by close examina- horizontal axes of the magnetometer. The field and orientation vari- tion of sonic waveforms during post-cruise processing. ations are shown in Figure 52. Each log was shifted in depth, by correlating the gamma-ray logs The horizontal magnetic component is degraded by sharp, very between runs, to correct for differences in the stretch of the logging high-amplitude variations. These variations were caused by the sen- cable. All logs were then corrected to depth as meters below sea floor sitivity of the horizontal component to changes in tool orientation. by subtracting the depth from rig floor to sea floor (4837.8 m). These Because the data are of such poor quality, they are not included in this depths should be accurate to within ±2 m. analysis. The abrupt changes in the tool orientation also affected the Depths for the temperature tool were determined using the pres- vertical magnetic field variations, but the amplitude of the vertical sure recorded in the instrument and a depth vs. pressure table derived magnetic field variations is much lower than that of the horizontal, from pressure readings at depths noted during logging. about 500 nT. The geochemical and spectral gamma-ray logs have been proc- Below the boundary between logging Units 4 and 5 (-490 mbsf), essed onshore and are discussed elsewhere (see "Onshore Geochemi- the vertical magnetic field gradually increases and then abruptly cal Processing" chapter, this volume). decreases at about 530 mbsf. The amplitude of this variation is almost SITE 869

Table 6. Concentrations of total, inorganic, and organic carbon and of total nitrogen and sulfur in sediments from Hole 869B.

Core, section. Depth Sample TC IC TOC CaCO, N S interval (cm) (mbsf) type" (%) (%) (7r) (7r)' (7r) (7r) TOC/N TOC/S Lithology

143-869B-

2R-1. 3-5 140.03 CARB 0.19 0.09 0.10 0.7 0.07 0.37 1.4 0.3 Brown chert 3R-CC, 10-12 149.70 CARB 0.23 0.11 0.12 0.9 0.06 0.45 2.0 0.3 Brown chert 4R-1, 15-16 159.45 CARB 0.14 0.04 0.10 0.3 0.12 0.34 0.8 0.3 Brown chert 4R-1,46-47 159.76 CARB 9.37 9.20 0.17 76.6 0.65 0.00 0.3 White siliceous chalk 4R-1.63-64 159.93 CARB 0.14 0.04 0.10 0.3 0.07 0.00 1.4 Beige chert 5R-1, 10-12 169.00 CARB 0.12 0.05 0.07 0.4 0.03 0.16 2.0 0.4 Yellow chert 6R-1,7-8 178.67 CARB 0.23 0.08 0.15 0.7 0.11 0.28 1.3 0.5 Beige chert 9R-CC, 11-12 207.71 CARB 5.81 5.73 0.08 47.7 0.10 0.33 0.8 0.2 Yellow claystone 1 OR-1.33-34 217.53 CARB 3.84 3.45 0.39 28.7 0.08 0.00 4.9 Tubiditic sand 10R-1, 145-150 218.65 IWSC 5.70 5.43 0.27 45.2 0.07 0.22 3.8 1.2 Light-brown claystone 10R-2, 45-16 219.15 CARB 7.89 7.56 0.33 63.0 0.09 0.00 3.6 Beige clayey mudstone 11R-1.88-89 227.78 CARB 3.23 2.S9 0.34 24.1 0.09 0.43 3.8 0.8 Brown claystone 11R-2. 145-150 229.85 IWSC 8.09 8.06 0.03 67.1 0.05 0.20 0.6 0.2 Light-gray clayey mudstone 11R-3, 62-63 230.52 CARB 4.88 4.87 0.01 40.6 0.10 0.25 0.1 0.0 Brown claystone 1IR-4. 129-131 232.69 CARB 0.93 0.60 0.33 5.0 0.06 0.47 5.5 0.7 Gray claystone 13 R-1.94-95 247.14 CARB 0.50 0.37 0.13 3.1 0.08 0.34 1.6 0.4 Volcanic turbiditic sand I3R-I. 145-150 247.65 IWSC 7.27 7.26 0.01 60.5 0.06 0.00 0.1 Beige clayey mudstone 13R-2. 87-88 248.57 CARB 3.98 3.72 0.26 31.0 0.12 0.00 2.1 Gray claystone 13R-2. 144-146 249.14 CARB 1.36 1.19 0.17 9.9 0.07 0.37 2.4 0.5 Gray-greenish claystone 13R-3. 30-32 249.50 CARB 10.01 10.00 0.01 83.3 0.10 0.00 0.1 White mudstone 13R-4. 51-52 251.21 CARB 7.59 7.26 0.33 60.5 0.10 0.26 3.3 1.2 Beige clayey mudstone I5R-I. 125-126 266.65 CARB 5.03 4.99 0.04 41.6 0.06 0.28 0.6 0.1 Gray claystone 15R-2. 127-128 268.17 CARB 3.12 3.10 0.02 25.8 0.01 0.18 2.0 0.1 Gray claystone 15R-4, 146-147 271.36 CARB 0.37 0.36 0.01 3.0 0.05 0.30 0.2 0.0 Volcanic turbiditic sand 15R-CC. 15-16 272.03 CARB 7.11 6.66 0.45 55.5 0.07 0.23 6.4 1.9 Beige clayey mudstone 16R-1.68-69 275.78 CARB 3.83 3.70 0.13 30.8 0.1 3 0.00 1.0 Beige claystone 16R-1.89-90 275.99 CARB 0.37 0.30 0.07 2.5 0.08 0.29 0.9 0.2 Volcanic turbiditic sand 17R-2. 0-5 285.83 IWSC 0.21 0.10 0.11 0.8 0.10 0.32 1.1 0.3 Volcanic turbiditic sand 17R-2. 21-22 286.04 CARB 0.28 0.19 0.09 1.6 0.04 0.18 2.0 0.5 Volcanic turbiditic sand 17R-2. 75-76 286.58 CARB 5.45 5.44 0.01 45.3 0.07 0.00 0.1 Gray claystone 17R-CC. 7-9 286.78 CARB 0.1 3 0. II 0.02 0.9 0.03 0.18 0.6 0.1 Volcanic turbiditic sand 19R-1.30-31 304.40 CARB 1.53 1.51 0.02 12.6 0.04 0.14 0.5 0.1 Volcanic turbiditic sand 19R-2. 10-11 305.70 CARB 2.83 2.34 0.49 19.5 0.11 0.31 4.4 1.6 Dark-gray claystone 20R-1. 12-13 313.92 CARB 1.00 0.77 0.23 6.4 0.05 0.00 4.6 Volcanic turbiditic sand 20R-2. 135-136 316.65 CARB 1.77 1.36 0.41 11.3 0.05 0.40 8.2 1.0 Gray claystone 2OR-2. 145-150 316.75 IWSC 1.17 0.99 0.18 8.2 0.23 0.95 0.8 0.2 Dark-gray claystone 2OR-3. 58-59 317.38 CARB 0.73 0.61 0.12 5.1 0.09 0.00 1.3 Dark-gray claystone 20R-CC. 12-13 318.98 CARB 1.67 1.65 0.02 13.7 0.05 0.00 0.4 Volcanic turbiditic sand 2IR-1.54-55 324.04 CARB 1.34 0.84 0.50 7.0 0.12 0.29 4.1 1.7 Volcanic turbiditic sand 22R-I, 102-103 334.12 CARB 0.78 0.50 0.28 4.2 0.19 0.S2 1.5 0.3 Gray claystone 22R-2. 8-9 334.68 CARB 2.52 2.49 0.03 20.7 0.21 0.93 0.1 0.0 Dark-gray claystone 23R-I. 115-116 343.95 CARB 0.32 0.06 0.26 0.5 0.18 0.79 1.4 0.3 Green sandy claystone 23R-I. 142-145 344.22 HS 2.17 2.12 0.05 17.7 0.06 0.22 0.8 0.2 Green-grayish claystone 23R-1. 145-150 344.25 IWSC 0.46 0.42 0.04 3.5 0.22 0.88 o.: 0.1 Green-grayish claystone 23R-2, 104-105 345.34 CARB 0.90 0.70 0.20 5.8 0.17 0.72 1.2 0.3 Volcanic turbiditic sand 25R-2. 104-105 364.74 CARB 3.26 3.09 0.17 25.7 0.21 0.83 0.8 0.2 Green claystone 26R-1.75-76 372.55 CARB 0.61 0.27 0.34 2 -i 0.29 1.33 1.2 0.3 Gray greenish claystone 26R-1. 109-110 372.89 CARB 0.45 0.18 0.27 1.5 0.21 0.90 1.3 0.3 Dark-gray sandy claystone 27R-1.6-7 381.56 CARB 0.40 0.03 0.37 0.2 0.28 1.12 1.3 0.3 Gray clayslone 27R-1.58-59 382.08 CARB 0.79 0.03 0.76 0.2 0.60 0.00 1.2 Beige claystone 27R-1.72-73 382.22 CARB 3.73 2.99 0.74 24.9 0.76 0.00 1.0 Beige calcareous claystone 28R-CC. 14-15 391.24 CARB 0.69 0.02 0.67 0.2 0.56 2.20 1.2 0.3 Gray claystone 29R-CC. 20-21 401.00 CARB 3.07 2.6X 0.39 22.3 0.54 2.14 0.7 0.2 Beige calcareous claystone 30R-1. 15-16 410.55 CARB 0.65 0.16 0.49 i.r 0.43 ().(X) 1.1 White sandy claystone 31R-1. 7-8 420.17 CARB 7.10 6.82 0.28 56.8 0.21 0.83 1.3 0.3 Calcareous sandstone 3IR-I. 81-82 420.91 CARB 2.51 2.43 0.08 202 0.22 0.90 0.4 O.I Volcanic turbiditic sandstone 3 IR-1.99-100 421.09 CARB 0.35 0.08 0.27 0.7 0.21 0.87 1.3 0.3 Brown claystone 3IR-1. 145-150 421.55 IWSC 3.32 3.10 0.22 25. 0.3 Sandy claystone 32R-1.67-68 430.47 CARB 1.12 0.42 0.70 3.5 0.20 0.84 3.5 0.8 Volcanic turbiditic sandstone 32R-1.70-72 430.50 CARB 1.15 1.04 0.1 1 8.7 0.20 0.82 0.6 0.1 Volcanic turbiditic sandstone 32R-2. 90-91 432.20 CARB 0.43 0.05 0.38 0.4 0.27 0.00 1.4 Brown claystone 33R-1. 17-18 439.57 CARB 3.27 3.03 0.24 25.2 0.31 0.00 0.8 Light-beige mudstone 33R-1.74-75 440.14 CARB 0.47 0.02 0.45 0.2 0.35 1.40 1.3 0.3 Beige claystone 33R-CC. 19-20 440.94 CARB 0.38 0.02 0.36 0.2 0.23 0.95 1.5 0.4 Gray claystone 34R-1.51-52 449.61 CARB 0.54 0.03 0.51 0.2 0.38 0.00 1.3 Gray claystone 34R-1.89-90 449.99 CARB 6.23 5.98 0.25 49. S 0.35 0.00 0.7 Light-gray mudstone 34R-2. 109-110 451.69 CARB 1.78 1.58 0.20 13.2 0.17 0.71 1.2 0.3 Gray claystone 34R-CC, 2-3 452.52 CARB 0.79 0.54 0.25 4.5 0.20 0.89 1.2 0.3 Gray claystone 35R-1. 7-8 458.87 CARB 0.04 0.04 0.00 0.3 0.03 0.00 0.0 Light-gray sandstone 35R-1.41^3 459.21 CARB 1.95 1.94 0.01 16.2 0.02 0.00 0.5 Gray-greenish sandstone 35R-1.78-80 459.58 CARB 0.04 0.02 0.02 0.2 0.08 0.00 0.2 Light-gray sandstone 36R-1, 25-26 468.65 CARB 0.69 0.12 0.57 1.0 0.05 0.00 11.0 Gray claystone 36R-1, 145-150 469.85 IWSC 1.25 1.03 0.22 8.6 0.03 0.00 7.3 Gray claystone 36R-2. 107-108 470.97 CARB 0.64 0.42 0.22 3.5 0.15 0.59 1.4 0.4 Gray claystone 36R-3, 5-7 471.45 CARB 0.45 0.30 0.15 2.5 0.16 0.67 0.9 0.2 Volcanic turbiditic sandstone 38R-1.53-54 488.23 CARB 1.10 1.05 0.05 8.7 0.04 0.00 1.0 Vole, sandstone with calcite veins 38R-3. 36-37 490.20 CARB 0.13 0.10 0.03 0.8 0.03 0.00 1.0 Volcaniclastic sandstone 38R-CC, 4-5 491.30 CARB 0.14 0.09 0.05 0.7 0.03 0.00 1.0 Volcaniclastic sandstone 39R-1, 128-129 498.68 CARB 0.16 0.15 0.01 1.2 0.03 0.00 0.3 Volcaniclastic sandstone 39R-CC, 8-9 500.20 CARB 0.15 0.10 0.05 0.8 0.02 0.00 2.0 Volcaniclastic sandstone 40R-1. 102-103 508.12 CARB 0.15 0.10 0.05 0.8 0.02 0.00 2.0 Coarse volcaniclastic sandstone

338 SITE 869

Table 6 (continued).

Core, section, Depth Sample TC IC TOC CaCO, N s a interval (cm) (mbsf) type (%) (%) (%) (%)' (%) (%) TOC/N TOC/S Lithology

41R-2, 116-117 519.46 CARB 0.14 0.09 0.05 0.7 0.03 0.00 1.0 Volcaniclastic sandstone 41R-4, 4-5 520.96 CARB 0.11 0.06 0.05 0.5 0.03 0.00 1.0 Coarse volcaniclastic sandstone 42R-1,64-65 527.04 CARB 0.16 0.09 0.07 0.7 0.03 0.00 2.0 Coarse volcaniclastic sandstone 42R-2, 67-68 528.52 CARB 0.12 0.09 0.03 0.7 0.03 0.00 1.0 Coarse volcaniclastic sandstone 42R-3, 30-31 529.65 CARB 0.11 0.08 0.03 0.7 0.04 0.00 0.7 Coarse volcaniclastic sandstone 42R-4, 33-34 530.99 CARB 0.10 0.07 0.03 0.6 0.03 0.00 1.0 Coarse volcaniclastic sandstone 43R-K85-86 536.95 CARB 0.17 0.12 0.05 1.0 0.02 0.00 2.0 Fine volcaniclastic sandstone 43R-2, 40-41 538.00 CARB 0.19 0.18 0.01 1.5 0.03 0.00 0.3 Fine volcaniclastic sandstone 44R-1,94-95 546.54 CARB 0.25 0.06 0.19 0.5 0.04 0.55 4.7 0.3 Coarse volcaniclastic sandstone 44R-2, 32-33 547.42 CARB 0.31 0.12 0.19 1.0 0.05 0.30 3.8 0.6 Fine volcaniclastic sandstone 44R-CC, 26-27 552.81 CARB 0.41 0.38 0.03 3.2 0.01 0.92 3.0 0.0 Fine volcaniclastic sandstone 45R-1,32-34 555.62 CARB 0.32 0.11 0.21 0.9 0.01 0.05 21.0 4.2 Coarse volcaniclastic sandstone 46R-1,77-78 565.37 CARB 0.34 0.13 0.21 I.I 0.01 0.21 21.0 1.0 Fine volcaniclastic sandstone 48R-1,32-33 584.22 CARB 1.24 1.09 0.15 9.1 0.03 0.30 5.0 0.5 Fine volcaniclastic sandstone 48R-CC, 15-16 584.67 CARB 6.60 6.53 0.07 54.4 0.03 0.13 2.0 0.5 Fine calcareous sandstone 49R-CC, 0-3 593.50 HS 0.95 0.81 0.14 6.7 0.03 0.17 4.6 0.8 Black argillaceous sandstone 49R-CC, 19-20 593.69 CARB 0.35 0.17 0.18 1.4 0.01 0.14 18.0 1.3 Fine volcaniclastic sandstone 50R-1, 1-2 603.21 CARB 0.43 0.15 0.28 1.2 0.01 0.19 28.0 1.5 Coarse volcaniclastic sandstone 50R-5, 1-3 609.21 CARB 0.60 0.23 0.37 1.9 0.01 0.61 37.0 0.6 Coarse volcaniclastic sandstone 50R-6, 134-135 612.04 CARB 2.30 1.66 0.64 13.8 0.05 0.25 13.0 2.5 Fine volcaniclastic sandstone 51R-1,56-57 613.26 CARB 3.43 3.02 0.41 25.2 0.04 0.00 10.0 Dark-gray sandy claystone 51R-1,72-73 613.42 CARB 7.19 7.14 0.04 59.5 0.01 0.10 4.0 0.4 Light-gray sandy mudstone 51R-3, 104-105 616.74 CARB 0.88 0.57 0.31 4.7 0.01 0.00 31.0 Brown sandy claystone 51R-4, 33-34 617.53 CARB 0.30 0.13 0.17 1.1 0.01 0.19 17.0 0.9 Dark-gray sandy claystone 52R-1, 146-148 623.86 CARB 0.23 0.08 0.15 0.7 0.01 0.11 15.0 1.3 Coarse volcaniclastic sandstone 52R-2, 113-115 625.03 CARB 1.40 0.97 0.43 8.1 0.04 0.03 11.0 14.0 Gray sandy claystone 52R-4, 2-4 626.92 CARB 0.77 0.52 0.25 4.3 0.01 0.09 25.0 2.8 Gray-greenish sandy claystone 53R-1,53-54 632.53 CARB 0.44 0.16 0.28 1.3 0.01 1.03 28.0 0.3 Coarse volcaniclastic sandstone 54R-1,88-91 642.68 CARB 0.20 0.12 0.08 1.0 0.01 0.09 8.0 0.9 Coarse volcaniclastic sandstone 54R-4, 63-65 646.60 CARB 0.19 0.09 0.10 0.7 0.01 0.02 10.0 5.0 Vole, sandstone with calcite veins 55R-2, 56-57 653.56 CARB 7.86 7.79 0.07 64.9 0.01 0.00 7.0 Light-gray sandy limestone 55R-3. 32-33 654.82 CARB 2.25 1.92 0.33 16.0 0.04 0.00 8.2 Green sandstone 56R-1,55-56 661.75 CARB 0.43 0.27 0.16 2.2 0.01 0.07 16.0 2.3 Dark-gray sandstone 56R-1,76-77 661.96 CARB 0.28 0.19 0.09 1.6 0.01 0.23 9.0 0.4 Green sandstone 56R-3, 63-64 664.83 CARB 0.23 0.05 0.18 0.4 0.01 0.09 18.0 2.0 Volcaniclastic sandstone 57R-1,31-33 671.01 CARB 0.27 0.09 0.18 0.7 0.01 0.05 18.0 3.6 Green sandstone 57R-2, 131-132 673.51 CARB 0.34 0.29 0.05 2.4 0.03 0.00 1.0 Gray sandstone 57R-3, 56-57 674.26 CARB 0.22 0.08 0.14 0.7 0.03 0.00 4.6 Green sandstone 57R-CC, 26-27 676.88 CARB 1.62 1.56 0.06 13.0 0.00 0.00 Green sandstone 58R-1,78-80 681.18 CARB 0.28 0.07 0.21 0.6 0.04 0.11 5.2 1.9 Coarse volcaniclastic sandstone 58R-5. 99-101 687.39 CARB 0.29 0.04 0.25 0.3 0.01 0.00 25.0 Coarse volcaniclastic sandstone 59R-1,56-58 690.56 CARB 0.28 0.18 0.10 1.5 0.01 0.00 10.0 Green sandstone 59R-1. 146-150 691.46 IWSC 0.10 0.08 0.02 0.7 0.00 0.01 2.0 Volcaniclastic sandstone 59R-3, 8-9 693.08 CARB 0.28 0.12 0.16 1.0 0.01 0.00 16.0 Green sandy claystone 59R-4, 3^t 694.53 CARB 0.33 0.06 0.27 0.5 0.01 0.18 27.0 1.5 Green sandstone 59R-5, 9-10 696.09 CARB 0.29 0.20 0.09 1.7 0.02 0.00 4.0 Green sandstone 60R-2, 84-86 700.84 CARB 0.21 0.05 0.16 0.4 0.07 0.00 2.3 Coarse volcaniclastic sandstone 60R-5, 79-80 705.29 CARB 0.26 0.05 0.21 0.4 0.02 0.00 10.0 Fine volcaniclastic sandstone 60R-7, 121-122 708.71 CARB 0.20 0.05 0.15 0.4 0.05 0.00 3.0 Coarse volcaniclastic sandstone 60R-8. 19-20 709.19 CARB 0.53 0.47 0.06 3.9 0.02 0.01 3.0 6.0 Sandy claystone 61R-I,46^7 709.86 CARB 0.53 0.06 0.47 0.5 0.19 0.00 2.5 Coarse volcaniclastic sandstone 61R-3, 51-54 712.91 CARB 0.17 0.05 0.12 0.4 0.01 0.01 12.0 12.0 Coarse volcaniclastic sandstone 62R-CC9-11 719.19 CARB 1.47 1.43 0.04 11.9 0.00 0.09 0.4 Gray calcareous sandstone 63R-2, 50-51 730.70 CARB 0.98 0.97 0.01 8.1 0.00 0.02 0.5 Fine green sandstone 63R-4, 80-81 734.00 CARB 0.10 0.07 0.03 0.6 0.00 0.02 1.0 Volcaniclastic sandstone 63R-6. 109-110 737.29 CARB 0.04 0.03 0.01 0.2 0.00 0.00 Volcaniclastic sandstone 63R-CC, 6-8 738.37 CARB 0.04 0.03 0.01 0.2 0.00 0.00 Volcaniclastic sandstone 64R-1. 115-116 739.55 CARB 0.08 0.04 0.04 0.3 0.01 0.08 4.0 0.5 Volcaniclastic sandstone 64R-2, 41-12 740.31 CARB 0.09 0.08 0.01 0.7 0.00 0.00 Green sandstone 64R-3, 49-50 741.89 CARB 0.04 0.04 0.00 0.3 0.00 0.00 Green sandstone 64R-5, 104-105 745.44 CARB 0.20 0.19 0.01 1.6 0.00 0.00 Green sandstone 65R-1, 17-18 748.07 CARB 1.36 1.33 0.03 11.1 0.00 0.00 Green sandstone 65R-2, 116-117 750.56 CARB 0.11 0.10 0.01 0.8 0.00 0.01 1.0 Green sandstone 65R-2, 125-126 750.65 CARB 0.27 0.27 0.00 2.2 0.00 0.00 Green sandstone 65R-2, 145-150 750.85 IWSC 0.38 0.37 0.01 3.1 0.00 0.00 Green sandstone 66R-1,3^ 757.63 CARB 0.09 0.08 0.01 0.7 0.00 0.00 Green sandstone 66R-2, 2-3 759.12 CARB 0.07 0.05 0.02 0.4 0.00 0.01 2.0 Volcaniclastic sandstone 66R-3, 60-61 761.20 CARB 0.11 0.06 0.05 0.5 0.00 0.00 Volcaniclastic sandstone 67R-1,76-77 768.06 CARB 0.08 0.08 0.00 0.7 0.00 0.08 0.0 Green sandstone 67R-2, 74-75 769.54 CARB 0.08 0.08 0.00 0.7 0.00 0.02 0.0 Green sandstone 67R-2, 98-99 769.78 CARB 0.14 0.13 0.01 1.1 0.00 0.00 Green sandstone 67R-4,42^3 772.22 CARB 0.04 0.04 0.00 0.3 0.00 0.00 Green sandstone 67R-5, 93-94 774.23 CARB 0.12 0.11 0.01 0.9 0.00 0.00 Green sandstone 68R-2, 54-55 778.94 CARB 0.68 0.66 0.02 5.5 0.00 0.00 Green sandstone 68R-4, 48-49 781.88 CARB 0.03 0.02 0.01 0.2 0.00 0.00 Green sandy claystone 68R-4, 61-62 782.01 CARB 8.25 7.90 0.35 65.8 0.01 0.00 35.0 Pale-green mudstone 68R-4, 65-66 782.05 CARB 0.03 0.03 0.00 0.2 0.00 0.00 Greenish-red laminated claystone 68R-4, 68-69 782.08 CARB 0.03 0.02 0.01 0.2 0.00 0.00 Green claystone 69R-1,55-56 787.15 CARB 1.40 1.31 0.09 10.9 0.00 0.08 1.0 Green calcareous sandstone 69R-2, 52-53 788.62 CARB 3.55 3.41 0.14 28.4 0.00 0.01 14.0 Green laminated mudstone 69R-2, 62-63 788.72 CARB 3.56 3.48 0.08 29.0 0.00 0.00 Green laminated mudstone

1 Sample type: CARB = carbonate; HS = headspace; IWSC = interstitial-water squeeze cake. SITE 869

CaCO3 (%) Lith. TOC (%) 0 0.2 0.4 0.6 0.8

20 40 60 80 units 1 1 100 . •j 1 ' 1 1 '

200 ~

IIIA 1 i | 300 50-

^400 r_ IIIB Q. E 01 •v :_ Q .Very NIC 100 —low — §"500 MID Low — _ • > HIE 600 p - 150 1 i 1 i I 700 b IMF Figure 42. Depth distribution of total organic carbon (TOC) concentrations in Hole 869A. 800' Figure 41. Depth distribution of calcium carbonate in Hole 869B.

100 1500 nT. This high-amplitude variation corresponds to lithological Subunit HID (487.8-536.1 mbsf) and is caused by volcaniclastic breccias. This high-amplitude variation is also concordant with the high intensity of magnetization of volcaniclastic breccias (Cores 143- 869B-40R through 143-869B-42R) determined from shipboard pa- leomagnetic studies. The increase of the vertical magnetic field com- ponent indicates that the volcaniclastic breccias have a negative inclination of magnetization. The high-amplitude, sharp increase at about 650 mbsf marks the boundary between logging Unit 5 and Unit 6. The character of vertical magnetic field variations in logging Unit 6 is different from that of logging Unit 5. Vertical magnetic field variations in logging Unit 6 exhibit long wavelengths (about 10 m) and relatively higher amplitude (about 500 nT). Logging Unit 6 corresponds to lithological Sub- unit IIIF (653.3-780.7 mbsf), a series of massive sandstone and silt- stone beds. These vertical magnetic field variations are probably caused by a succession of sandstone-siltstone sequences. Clear bound- aries between logging Units 2, 3, and 4 are not observed from vertical magnetic field variations. 700 - The arrows in Figure 52 indicate the normal-reverse polarity boundary inferred from vertical magnetic field variations and ship- board paleomagnetic results. The upper arrow shows the boundary 800 between Chrons 33N and 33R and the lower one between Chron 33R and the Cretaceous normal superchron. The boundary between 33N Figure 43. Depth distribution of total organic carbon (TOC) concentrations in and 33R lies at about 330 mbsf and that between 33R and the Hole 869B. Cretaceous normal superchron is at about 410 mbsf. The character of the vertical magnetic variations indicated by the arrows in Fig- the boundaries between Chrons 33N, 33R, and the Cretaceous nor- ure 52 are different from those below and above the arrows. The mal superchron. vertical magnetic variations at the arrows show abrupt decreases and longer wavelengths (about 10 m) than those below and above the Log-based Units arrows, respectively. The average trend of the vertical magnetic field variations between the arrows seems to be lower than that above the Six logging units were identified using the geophysical and geo- upper arrow and below the lower arrow. Shipboard paleomagnetic chemical logs. These units are defined primarily on the basis of the results indicate that the boundary between 33N and 33R lies between resistivity, velocity, density, and gamma-ray logs. Cores 143-869B-20R (313.8-323.5 mbsf) and 143-869B-21R (323.5-333.1 mbsf). Paleomagnetic results also show that the bound- Logging Unit 1 (Base of Pipe, 89.0-224.2 mbsf) ary between 33R and the Cretaceous normal superchron is probably located near Core 143-869B-32R (429.8-439.4 mbsf). These results Logging Unit 1 corresponds to lithologic Unit II, an interval of por- suggest that the vertical magnetic field shown by the arrows indicates cellanite associated with clayey nannofossil and radiolarian oozes.

340 SITE 869

Table 7. Results of the Geofina hydrocarbon meter analyses and concentrations of carbonate, total organic carbon, and nitrogen for selected samples from Hole 869B.

Core, section. Depth Sample CaCO, TOC Tn N a interval (cm) (mbsf) type Lithology (%) (%) GHM aXRE s, S2 HI (%) TOC/N

143-869B- 15R-CC, 15-16 272.03 CARB Beige claystone 55.5 0.45 0.07 6.4 19R-2, 10-11 305.70 CARB Dark gray claystone 19.5 0.49 0.11 4.5 20R-2, 135-136 316.65 CARB Gray claystone 11.3 0.41 405 345 0.16 0.24 58 0.05 8.2 21R-1,54-55 324.04 CARB Volcaniclastic sandstone 7.0 0.50 0.12 4.2 27R-1,6-7 381.56 CARB Gray claystone 0.3 0.37 425 365 0.05 0.03 8 0.28 .3 27R-1,72-76 382.22 CARB Beige calcareous claystone 24.9 0.74 514 454 0.02 0.20 26 0.76 .0 28R-CC, 14-15 391.24 CARB Gray claystone 0.2 0.67 0.56 2 30R-1, 15-16 410.55 CARB White sandy claystone 1.3 0.49 0.43 .1 33R-1,74-75 440.14 CARB Beige claystone 0.2 0.45 0.35 .3 34R-2, 109-110 451.69 CARB Gray claystone 13.2 0.20 0.17 .2 36R-1,25-26 468.65 CARB Gray claystone 1.0 0.57 443 383 0.04 0.10 17 0.05 11.4 51R-1,56-57 613.26 CARB Dark gray sandy claystone 3.0 0.41 0.04 10.3

a Sample type: CARB = carbonate. Note: S, = free hydrocarbons; S , = pyrolyzable hydrocarbons (both in mg hydrocarbons/g of rock), HI = hydrogen index (in mg hydrocarbons/g TOC), blank space indicates no clear data or below the detection threshold of GHM.

Logging Subunit la (Base of Pipe, 89.0-165.2 mbsf) this unit probably result from the presence of thin chert layers or layerlike concentrations of nodules. Chert and porcellanite fragments Based on log responses alone, the nannofossil oozes of logging were recovered in Cores 143-869B-22R and -24R. The situation in this Subunit 1 a are homogeneous, with only minor intervals of porcellanite zone appears to fit the case where a shallow resistivity response of and chert to a depth of 139.2 mbsf. The first significant chert intervals greater amplitude, both higher and lower than the other two resistivity occur from 139.2 to 142.6 mbsf; the lithologies above and below this measurements, suggests the presence of thin layers. This effect is interval appear similar based on log responses. The base of this subunit highlighted in Figure 53. The differences between the three resistivity is clearly defined by all geophysical logs. Resistivity values within the log types are attributed here to the different depths of investigation, but oozes of Subunit 1 a range from 0.4 to 0.5 ohm-m. Except for cherty 3 the differences are accentuated by the large hole diameter. intervals, density is less than 1.4 g/cm for the entire interval to Although the overall lithologies, dominantly claystone with minor 165.2 mbsf. Gamma-ray counts are uniformly 0 to 5.0 API units. intercalations of volcaniclastic sandstone, are similar to those of logging Unit 2, logging Unit 3 may represent a subtle change in Logging Subunit lb (165.2-224.2 mbsf) depositional environment, from low energy, infrequent, distal tur- Logging Subunit 1 b corresponds to the lower portion of lithologic bidites that are heavily bioturbated in logging Unit 2, to high energy, Unit II. A stepwise increase in resistivity, from 0.4 to 1.6 ohm-m, and more frequent influxes in logging Unit 3. density, from 1.4 to 2.0 g/cm3, defines the top of this subunit. Por- cellanite is the dominant lithology of the uppermost portion; numer- Logging Unit 4 (402.2-487.2 mbsf) ous porcellanite intervals of varying thickness alternate with the radiolarian oozes that are typical of the lower part of Subunit 1 b. Total Logging Unit 4 corresponds to most of lithologic Subunit IIIB and gamma rays (SGR in Fig. 50) increase downhole, whereas density all of Subunit IIIC. Recovered lithologies are similar for both of these and resistivity decrease, reflecting the increasing clay content of Sub- subunits. The top and base of this coarsening-upward unit are defined unit lb sediments. by sharp changes in the gamma-ray log. The coarse fraction at the top of the unit is the volcaniclastic sand common in logging Units 2 and 3. The interval from 412.2 to 442.0 mbsf is heavily bioturbated and has Logging Unit 2 (224.2-302.3 mbsf) a uniform resistivity response of about 1.1 ohm-m. The high-gamma- Logging Unit 2 corresponds to the upper portion of lithologic Sub- ray, conductive basal portion of logging Unit 4 is probably an ashy unit IIIA (207.7-381.5 mbsf), a series of intercalated claystones and layer, judging from the broad peak in potassium abundance (Fig. 50). volcaniclastic silts and fine sands. This unit is heavily bioturbated, hence the uniform appearance on the resistivity log. Resistivity de- Logging Unit 5 (487.3-654.4 mbsf) creases slightly downhole from 1.9 to 1,0 ohm-m; density decreases to very low values at the base of logging Unit 2. Logging Unit 5 corresponds to lithologic Subunits HID (487.8- 536.1 mbsf) and HIE (536.1-653.3 mbsf). Unit 5 is bounded at the Logging Unit 3 (302.3-402.2 mbsf) top and bottom by large fining-upward sequences: the first from 487.2 to 534.0 mbsf (Cores 143-869B-38R through -42R) and the second Logging Unit 3 corresponds to the lower part of lithologic Subunit from 625.8 to 654.2 (Cores 143-869B-52R through Section 143- IIIA (207.7-381.5 mbsf) plus the upper 20 m of lithologic Subunit IIIB 869B-55R-2; Fig. 54). The lower contact of the coarse basal breccias (381.5^158.8 mbsf). The top of this unit is defined by sharp increases of the second sequence with the underlying silty claystone is promi- in gamma, resistivity and density logs. Logging Unit 3 is a very nent in the photograph of Core 143-869B-55R (Fig. 55). In both heterogeneous interval having many thin, alternately resistive and sequences, the resistivity decreases in a stepwise fashion (Fig. 48); conductive intercalations; resistivity values range from 1.0 to 4.9 ohm- the lithologies corresponding to these stepped decreases in resistivity m for most of the unit. Near the base of the unit is a thick (378.8- form sharp contacts that are also documented in the core material. 393.1 mbsf) interval displaying uniformly low gamma-ray counts, Isolated, thin, conductive events in the coarse sandstones and breccias medium-high resistivity, high density, and very high silicon content (Bouma "A" unit) probably correspond to concentrations of claystone (Fig. 51). Although recovery in this interval was poor, logging results and/or siltstone clasts. Isolated resistive events in the massive sand- indicate that it is probably a cherty interval. Similarly, the numerous stones may be caused by local concentrations of zeolite cement, which minor excursions to high resistivity and density occurring throughout in turn is caused by alteration of volcanic glass.

341 SITE 869

Table 8. Index property data for Holes 869A and 869B.

Water Bulk Grain Water Bulk Grain Core, section. Depth content density density Porosity Core, section. Depth content density density Porosity 3 1 interval (cm) (mbsf) (%) (g/cm) (g/crr/) (%) interval (cm) (mbsf) (%) (g/cm ) (g/cπr ) (%)

143-869 A- 143-869B-

1H-1,77-79 0.77 174.40 1.34 2.63 83.40 31R-1,97-99 421.08 29.14 1.87 2.51 42.21 1H-5, 74-76 6.74 360.70 .24 2.02 95.00 32R-1,65-67 430.46 34.85 1.86 2.65 48.01 2H-1,77-79 10.47 219.80 .28 2.45 85.60 32R-1.86-88 430.67 26.27 1.95 2.61 40.66 2H-3, 76-78 1346 62.00 .67 2.72 62.40 32R-2, 87-89 432.18 34.16 1.81 2.50 46.10 3H-I, 106-107 20.26 83.10 .55 2.66 68.60 33R-1. 16-18 439.57 26.06 1.93 2.55 39.93 3H-2. 99-101 21.69 126.90 .42 2.60 77.40 33R-CC. 17-18 440.93 31.84 1.83 2.49 44.26 4H- . 75-77 29.45 55.90 .56 2.62 54.40 34R-1,87-89 449.98 13.95 2.15 2.57 26.36 4H-6. 60-62 36.80 105.80 .66 2.67 83.40 34R-2, 111-113 451.72 23.99 2.07 2.78 40.00 5H-4. 75-77 43.45 56.90 .71 2.72 60.60 34R-3, 31-33 452.42 22.78 2.07 2.74 38.43 6H-4. 74-76 52.94 54.20 .72 2.69 58.90 35R-1, 13-14 458.94 27.82 1.92 2.57 41.70 7H-2, 39-41 57.71 57.90 .70 2.69 60.90 35R-1, 41-44 459.23 9.39 2.28 2.60 19.60 7H-2, 75-77 58.07 65.30 .67 2.71 64.30 36R-1,25-27 468.66 20.41 2.10 2.72 35.68 7H-6. 74-76 64.06 46.60 .86 2.71 57.70 36R-2. 105-107 470.96 28.21 1.97 2.72 43.38 8H-3, 78-80 69.03 49.40 .77 2.69 57.20 36R-3, 4-6 471.45 26.82 2.07 2.90 43.71 8H-6, 87-89 73.62 54.30 .76 2.69 60.30 38R-1,51-53 488.22 25.28 2.01 2.69 40.50 8H-8, 72-74 76.47 49.10 .79 2.69 57.50 38R-3, 34-36 490.19 20.98 2.07 2.67 35.92 9H-2, 78-80 78.48 57.00 .72 2.72 61.10 38R-CC, 2-4 491.29 19.33 2.11 2.69 34.18 9H-4, 79-81 81.49 107.20 .46 2.54 74.00 39R-I, 126-128 498.67 26.54 2.01 2.75 42.23 9H-6, 77-79 84.47 112.70 .53 2.26 78.90 39R-CC, 7-9 500.20 18.80 2.16 2.76 34.17 1 OX-1,71-73 86.41 112.40 .50 2.53 77.30 41R-2. 118-120 517.99 14.81 2.06 2.44 26.55 10X-2, 69-71 87.89 90.40 .43 2.65 66.40 41R-4. 9-11 521.02 10.71 2.16 2.46 20.85 10X-CC, 6-8 88.36 1.85 ..15 2.20 3.91 42R-I, 110-112 527.51 12.52 2.12 2.46 23.56 11X-2. 83-85 97.83 114.30 .41 2.42 73.30 42R-4, 19-21 530.86 12.15 2.19 2.55 23.68 I1X-4, 37-39 100.37 129.40 .37 2.39 75.50 43R-1.83-85 536.94 19.38 2.12 2.71 34.46 12X-1,60-62 106.10 82.90 .53 2.55 67.80 43R-2, 38-40 537.99 21.63 2.08 2.71 36.93 12X-4, 68-70 110.68 201.90 .25 2.11 81.40 44R-1,94-96 546.55 5.49 2.45 2.66 12.74 13X-2. 20-22 117.20 222.50 .34 2.09 90.30 44R-2, 33-34 547.44 21.84 2.06 2.68 36.92 13X-4, 52-54 120.52 210.90 .23 2.08 81.50 44R-CC. 26-28 551.87 19.56 2.10 2.68 34.43 14X-3, 40-42 128.90 171.90 .29 2.18 79.60 45R-1,32-34 555.63 7.93 2.38 2.67 17.45 14X-5, 44-^6 131.94 212.90 .24 2.07 82.30 45R-CC, 19-21 561.96 19.67 2.13 2.75 35.08 15X-2, 68-70 137.68 199.50 .25 2.07 81.50 46R-1,76-79 565.38 25.77 2.01 2.72 41.20 15X-6, 32-34 143.32 145.60 .34 2.19 77.60 48R-1,44-46 584.37 24.55 2.01 2.67 39.58 50R-1,2-5 603.24 19.80 2.15 2.78 35.48 143-869B- 50R-5, 1-3 609.22 19.28 2.14 2.75 34.64 50R-6, 126-128 611.97 23.68 2.03 2.69 38.95 2R-1,3-6 140.07 6.89 2.15 2.33 13.86 51R-1,55-57 613.26 15.75 2.22 2.74 30.17 3R-CC, 10-13 149.18 1.53 2.45 2.51 3.70 51R-3. 104-106 616.75 23.76 2.04 2.72 39.23 4R-I, 16-17 159.46 57.83 1.50 2.11 55.02 51R-4. 33-35 617.54 28.45 1.96 2.69 43.34 4R. 1,45^6 159.75 110.05 1.43 2.72 74.96 52R-I, 146-148 623.87 17.60 2.13 2.66 31.87 4R-1,62-63 159.92 0.94 2.43 2.47 2.28 52R-2, 113-115 625.04 19.01 2.13 2.71 34.03 5R-1, 10-12 169.01 1.46 2.54 2.60 3.65 52R-4, 2-4 626.93 20.77 2.08 2.68 35.76 6R-1, 5-7 178.12 7.57 2.04 2.22 14.38 53R-2, 53-55 635.44 19.79 2.05 2.58 33.84 11R-4, 1-3 231.42 41.87 1.85 2.88 54.68 54R-1,91-93 642.72 13.53 2.17 2.59 25.91 13R-4. 52-54 251.00 31.13 1.96 2.80 46.60 54R-4. 36-38 646.34 9.89 2.25 2.57 20.26 15R-1, 124-127 266.65 62.64 ] .66 2.84 64.03 54R-6, 108-110 650.06 12.96 2.21 2.63 25.41 15R-4. 144-146 271.35 43.12 1.87 2.99 56.30 55R-2, 56-58 653.57 12.85 2.23 2.65 25.42 15R-CC. 13-16 272.00 32.01 1.95 2.80 47.24 55R-3, 31-33 654.82 14.62 2.21 2.68 28.13 16R-1,66-68 275.77 31.65 2.01 2.96 48.40 55R-3, 111-113 655.62 17.72 2.10 2.61 31.63 16R-1,90-92 276.01 89.36 1.52 2.85 71.81 55R-5, 48-50 657.99 22.19 2.04 2.65 36.98 17R-2, 76-78 285.57 7.46 2.58 2.93 17.94 56R-1.79-81 662.00 20.65 2.08 2.67 35.53 17R-CC. 6-8 286.78 29.10 1.99 2.80 44.92 56R-2. 115-117 663.86 8.82 2.03 2.24 16.47 19R-1,28-30 304.39 78.93 1.55 2.77 68.58 56R-3, 70-72 664.91 12.59 1.89 2.13 21.16 19R-2. 9-11 305.70 12.52 2.32 2.78 25.84 57R-1,31-33 671.02 21.68 2.03 2.62 36.19 20R-1. 13-15 313.94 21.83 2.12 2.80 37.94 57R-2, 131-133 673.52 21.22 2.04 2.61 35.63 20R-2, 136-138 316.67 68.82 1.61 2.79 65.72 57R-3. 56-57 674.27 24.69 2.00 2.66 39.66 2OR-3, 57-59 317.38 67.98 1.60 2.69 64.64 57R-CC, 16-17 675.37 12.56 2.23 2.64 24.89 20R-CC, 12-14 318.43 29.10 1.96 2.71 44.10 5 8R-1,78-80 681.19 15.42 2.03 2.41 27.12 21R-1. 19-21 323.70 28.01 2.00 2.79 43.87 58R-5, 99-101 687.40 8.70 2.00 2.20 16.04 22R-3, 22-24 335.83 27.06 2.00 2.74 42.56 59R-1,56-58 690.57 26.20 1.94 2.58 40.30 23R-1, 114-116 343.95 88.10 1.47 2.52 68.96 59R-3, 7-9 693.08 22.55 2.03 2.65 37.43 23R-2, 103-105 345.34 23.64 2.07 2.78 39.68 59R-4, 2-4 694.53 21.58 2.05 2.66 36.44 25R-2. 4-6 363.75 31.59 1.93 2.73 46.32 59R-5. 8-10 696.09 19.42 2.04 2.55 33.15 25R-2. 104-106 364.75 40.39 1 .S3 2.75 52.61 60R-2, 84-86 700.85 12.73 2.09 2.43 23.63 25R-3. 75-77 365.96 20.77 2.08 2.68 35.79 60R-5, 81-83 705.32 16.42 2.15 2.65 30.32 26R-1,33-35 372.14 32.28 1.92 2.73 46.81 60R-7, 122-124 708.73 17.37 2.12 2.63 31.37 26R-1,73-75 372.54 74.79 1.56 2.70 66.86 60R-8, 20-22 709.21 28.69 1.92 2.61 42.79 27R-1, 7-9 381.58 21.21 1.97 2.48 34.50 61R-1, 44-46 709.85 25.04 1.99 2.65 39.86 27R-1,55-57 382.06 13.23 2.02 2.34 23.65 61R-2, 48-50 709.47 10.27 2.09 2.36 19.52 27R-1,70-72 382.22 13.34 2.05 2.38 24.09 63R-2,48-50 730.69 18.40 2.10 2.63 32.57 28R-CC, 12-14 391.23 12.31 2.08 2.40 22.80 63R-3, 74-76 732.45 25.68 1.95 2.58 39.82 29R-CC, 21-23 40L03 13.84 2.14 2.53 25.97 63R-4, 78-80 733.99 20.66 2.04 2.61 35.00 30R-1. 12-14 410.53 15.89 2.08 2.50 28.46 63R-6, 109-111 737.30 3.90 2.09 2.19 7.86 31R-1.5-7 420.16 25.03 2.01 2.68 40.17 63R-CC, 6-8 738.38 3.58 2.16 2.25 7.46 31R-1.82-84 420.93 32.47 .92 2.73 47.00 64R-1. 112-114 739.53 15.78 2.12 2.57 28.88

342 SITE 869

Table 8 (continued).

Water Bulk Grain Water Bulk Grain Core, section, Depth content density density Porosity Core, section. Depth content density density Porosity interval (cm) (mbsf) (%) (g/crr/) (g/cm3) (%) interval (cm) (mbsf) (%) (g/cm-) (g/crrv) (%)

143-869B- 143-869B-

64R-2. 38-40 740.29 23.49 1.99 2.59 37.87 67R-2. 72-74 769.53 12.49 2.20 2.59 24.47 64R-3, 46-48 741.87 24.96 1.96 2.57 39.05 67R-2, 96-98 769.77 30.69 1.90 2.62 44.61 64R-4, 78-80 743.69 22.61 2.04 2.67 37.62 67R-4, 40-42 772.21 24.2 2.02 2.68 39.36 64R-5, 105-107 745.46 27.25 1.92 2.56 41.12 67R-5, 91-93 774.22 28.70 1.93 2.63 42.99 64R-6, 125-127 747.16 22.29 2.00 2.58 36.50 67R-6, 50-52 775.31 26.27 1.96 2.63 40.87 65R-1. 14-17 748.05 24.32 1.99 2.62 38.91 68R-1,58-60 777.49 27.52 1.95 2.63 42.03 65R-2. 115-117 750.56 22.18 2.04 2.65 37.00 68R-2, 48-50 778.89 22.47 2.03 2.63 37.17 65R-2, 123-125 750.64 25.30 1.96 2.60 39.64 68R-3, 67-69 780.58 22.34 2.02 2.62 36.91 65R-3, 14-16 751.05 23.41 2.04 2.69 38.62 68R-4, 57-59 781.98 9.67 2.36 2.71 20.79 65R-CC, 17-19 752.58 25.10 1.97 2.61 39.62 68R-5, 58-60 783.49 19.19 2.06 2.58 33.15 66R-1,2-4 757.63 20.95 2.04 2.62 35.40 69R-1.7-9 786.68 9.02 2.35 2.68 19.46 66R-2, 2-4 759.13 16.69 2.06 2.50 29.46 69R-1, 144-146 788.05 22.11 2.04 2.64 36.88 66R-3, 59-61 761.20 19.90 2.09 2.67 34.72 69R-2, 21-23 787.94 20.27 2.09 2.68 35.23 67R-1, 74-76 768.05 21.20 2.04 2.61 35.60

The intervening portion of logging Unit 5 contains numerous thanks to the good core recovery through much of the section, and to fining- and coarsening-upward sequences at various scales. Bed good-quality downhole logs. In many places, the logs, particularly the thickness varies between 1 (the lower bound on resolution of the resistivity log, can be matched directly against lithologic contacts in resistivity tool) to 12 m. Many of the large fining/coarsening-upward the cores themselves. sequences are composed of smaller sequences. Some sequences ter- The best seismic profile through Site 869 is the line run by the minate in a thin, conductive, high-gamma-ray level and probably Thomas Washington, during the Tunes Expedition, Leg 8, a section correspond to the claystone, or "E" unit, of the Bouma sequence. of which is shown as Figure 56. The main reflectors in this profile are The sharp peak in gamma rays at 615.7 mbsf coincides with the presented in Table 12. depth at which recovery of coalified woody fragments was reported Between the seafloor and the first prominent reflector (Reflec- in Interval 143-869B-51R-4 at 25-40 cm. tor Cl), the reflection patterns are irregular, suggesting broad chan- nels. The seafloor itself, as seen in the 3.5-kHz record taken by the Logging Unit 6 (654.4-770.0 mbsf) JOIDES Resolution during the approach to Site 869 (Fig. 10), shows an erosional surface that truncates beds at the seafloor. Logging Unit 6 corresponds to lithologic Subunit IIIF (653.3- One is tempted to place Reflector C1, at about 0.085 s two-way 780.7 mbsf), a series of massive sandstone and siltstone beds. The traveltime (twtt) below the seafloor (bsf) at the first porcellanite resistivity log indicates that logging Unit 6 is a highly heterogeneous encountered in Hole 869A, at 97 cm in Section 2 of Core 143-869A- interval having numerous thin, conductive intercalations (massive 10X. This core was taken between 85.7 and 95.5 mbsf, and the siltstones) separating the highly resistive peaks of the compact, well- "Geolograph" shows a marked slowing of penetration at about cemented sandstones. Many of the beds of this succession of sand- 90 mbsf. The downhole logs show a marked increase in velocity and stone-siltstone sequences exhibit sharp lower contacts; in many places, resistivity between about 89 and 91 mbsf, just below the bottom of the erosive nature of these contacts is revealed in recovered core the BHA during logging Run 1. The interval velocity, from Reflec- material as siltstone clasts contained in the bases of the overlying tor Cl to the seafloor, assuming the reflector is at 90 mbsf, would be sandstone units. Upper contacts appear gradational in the resistivity about 2.1 km/s, which is much faster than velocities of about 1.6 km/s and density logs. Bed thickness varies from about 1 to 9 m. Fairly good recorded in the sonic log from strata immediately below this reflector, correlation between logs and core can be made through the FMS in from about 90 to 150 mbsf. laminated intervals with parallel boundaries, where there is probably On the other hand, if we assume that 1.6 km/s is roughly the correct little or no current influence. interval velocity for the strata above Reflector C1, then the calculated depth to the reflector would be at about 70 mbsf. Because of the Summary interference of the BHA when logging the shallow subsurface section, we cannot know if another interval exists higher up in the stratigraphic The sedimentary strata recovered at Site 869 show stratigraphic column that shows an impedance contrast that could create Reflec- variation caused by downhole changes in the amount, texture, and tor C1. The only significant change in lithology was found in Cores composition of volcaniclastic materials and composition of biogenic 143-869A-7H and -8H (57.2-76.2 mbsf), where clayey nannofossil influx. In the lower portion of the hole, where recovery in the ooze occurs, in contrast to the nannofossil ooze above and the volcaniclastics is good, correlations among the cores and logs can radiolarian nannofossil ooze below. It is possible that an impedance be done on a section-by-section basis. The downhole measurements contrast at the base or top of this interval might account for Reflec- have been interpreted here with respect to the stratigraphic column tor Cl. Reflector Cl shows up in the 3.5-kHz profile (see "Site as defined by the cores. Because the total recovery was only 20% in Geophysics" section, this chapter); thus, it represents a marked, shal- the upper, cherty units, such an interpretation is also valuable and low change in acoustic impedance. necessary for defining unit thicknesses and boundaries with preci- The reflector indicates an irregular, hummocky form in the seismic sion, and to check that no major lithologic event was missed as a profile (Fig. 56), which suggests either an erosional unconformity result of partial recovery. near the Oligocene/Eocene boundary or preservation of a hummocky surface on large, dunelike bed forms, having a wavelength of about SEISMIC STRATIGRAPHY 1 km and a height of about 10 to 20 m. Reflector C2, at about 0.165 s twtt bsf, has been placed at the top The seismic stratigraphy at Site 869, at least down to the level of of the interval showing markedly higher resistivity and velocity, at the last cores recovered, at 796.2 mbsf, is relatively straightforward, 141 to 144 mbsf in the downhole log. In the cores, this is within SITE 869

Table 9. Sonic velocity, anisotropy, and bulk density data for Holes 869A and 869B.

Anisotropy Anisotropy Bulk Core, section, Depth V (cu) Vpl (cu) Vpl (me) Vpl (me) (cu) (me) density interval (cm) (mbsf) (km/s) (km/s) (km/s) (km/s) (%) (%) (g/cm3)

143-869 A-

10X-CC, 6-8 88.36 4.102 3.950 3.772 2.15

2R-1.3-6 140.07 3.415 5.193 -41.302 2.15 3R-CC, 10-13 149.18 4.763 4.846 -1.730 2.45 4R-I, 16-17 159.46 4.132 3.578 14.362 1.50 4R_l.45^6 159.75 2.448 2.068 16.860 1.43 4R-1.62-63 159.92 4.671 4.913 -5.052 2.43 5R-1, 10-12 169.01 5.053 4.243 17.422 2.54 6R-I.5-7 178.12 3.232 3.279 -1.462 2.04 9R-CC. 3-5 207.64 2.944 HR-4, I-3 231.42 1.810 1.721 5.030 1.85 13R-4, 52-54 251.22 1.767 1.675 5.293 1.96 15R-1, 124-127 266.65 (1) 1.66 15R-2, 127-130 268.19 (2) 1.250 (1) 15R.4, 144-146 271.35 1.308 1.053 21.607 1.87 15R-CC, 13-16 272.03 1.95 16R-1,66-68 275.77 1.686 1.431 16.362 2.01 16R-1.90-92 276.01 2.245 2.062 8.507 1.52 16R-1.92-94 276.03 2.142 17R-2. 76-78 285.57 1.589 1.415 11.583 2.58 17R-CC. 3-5 286.78 2.240 2.194 2.052 1.99 19R-1, 28-30 304.39 2.854 2.750 3.700 1.55 19R-2. 9-11 305.70 1.743 1.665 4.624 2.32 19R-2, 23-26 305.85 .702 20R-1. 13-15 313.94 2.753 2.688 2.386 2.12 20R-2, 136-138 316.67 1.905 1.745 8.771 1.61 20R-3, 57-59 317.38 1.832 1.749 4.622 1.60 20R-CC. 12-14 318.43 2.403 2.404 -0.044 1.96 2IR-1, 19-21 323.70 2.00 22R-2. 6-8 334.67 1.917 1.843 3.916 22R-3. 0-4 335.62 2.667 22R-3, 22-24 335.83 2.614 2.517 3.801 2.00 23R-1, 114-116 343.95 1.784 1.718 3.741 1.47 23R-2, 103-105 345.34 2.640 2.600 1.505 2.07 25R-2, 4-6 363.75 2.591 2.575 0.643 1.93 25R-2. 78-81 364.50 2.011 25R-2, 104-106 364.75 1.804 1.695 6.175 1.83 25R-2, 109-112 364.81 (1) 25R-3. 75-77 365.96 1.960 1.766 10.450 2.08 26R-1,33-35 372.14 2.447 2.434 0.558 1.92 26R-1,73-75 372.54 1.898 1.819 4.201 1.56 27R-1,7-9 381.58 2.627 2.439 7.421 1.97 27R-1,55-57 382.06 3.502 2.735 24.591 2.02 27R-1,70-72 382.22 3.278 3.019 8.222 2.05 28R-CC, 12-14 391.23 3.359 2.559 27.041 2.08 29R-CC. 21-23 401.03 3.384 3.126 7.9 302.14 30R-CC. 12-14 410.53 3.143 2.951 6.314 2.08 31R-1.5-7 420.16 2.358 2.383 -1.038 2.01 31R-1,82-84 420.93 1.889 1.870 0.992 1.92 31R-1,97-99 421.08 2.262 2.208 2.406 1.87 32R-1,65-67 430.46 1.956 1.880 3.928 1.81 32R-1,86-88 430.67 2.296 2.013 13.140 1.86 32R-2, 87-89 432.18 2.278 2.078 9.202 1.95 33R-1, 16-18 439.57 2.443 2.346 4.037 1.93 33R-2. 17-18 440.93 2.330 2.166 7.291 1.83 34R-1,87-89 449.98 3.309 3.199 3.383 2.15 34R-2, 107-110 451.68 2.075 34R-2. 111-113 451.72 2.253 2.069 8.525 2.07 34R-2. 113-117 451.75 2.101 1.092 34R-3, 31-33 452.42 2.373 2.222 6.568 2.07 35R-1, 13-14 458.94 2.374 2.286 3.763 1.92 35R-1,24-26 459.05 2.642 35R-1, 41-44 459.23 3.647 3.205 12.913 2.28 36R-1,25-27 468.66 2.419 2.210 9.019 2.10 36R-2. 105-107 470.96 2.126 1.977 7.279 1.97 36R-3, 4-6 471.45 2.076 2.098 -1.021 2.07 36R-3, 115-118 472.55 (1) 38R-1, 51-53 488.22 2.283 2.324 -1.768 2.01 38R-2, 25-27 488.60 (1) 38R-2. 29-31 488.65 2.359 38R-3. 34-36 490.19 2.897 2.914 -0.605 2.07 38R-CC. 2-4 491.29 2.11 39R-1, 126-128 498.67 2.576 2.730 -5.811 2.01

344 SITE 869

Table 9 (continued).

Anisotropy Amsotropy Bulk Core, section. Depth Vpl (cu) V, (cu) Vpl (me) Vp, (me) (cu) (mc) density interval (cm) (mbsf) (km/s) (km/s) (km/s) (km/s) (%) (9<) (g/cm3)

39R-CC, 7-9 500.20 3.233 3.028 6.540 2.16 40R-1, 101-102 508.12 3.282 3.336 -1.621 40R-2, 36-38 508.97 3.232 -3.525 40R-2, 40-42 509.01 3.348 40R-3, 5-7 510.16 3.177 3.145 0.999 41R-2. 114-118 517.96 3.794 41R-2, 118-120 517.99 4.074 3.985 2.198 2.06 41R-4, 0-5 520.95 4.055 41R-4, 5-7 520.98 4.262 4.978 41R-4. 9-11 521.02 4.111 3.974 3.391 2.16 42R-1, 107-109 527.48 3.778 42R-1, 110-112 527.51 4.044 3.773 6.927 2.12 42R-1, 112-116 527.54 3.962 42R-4, 19-21 530.86 3.726 4.021 -7.609 2.19 43R-1,83-85 536.94 2.710 2.568 5.408 2.12 43R-2, 38-40 537.99 2.658 2.557 3.889 2.08 44R-1,94-96 546.55 4.630 4.733 -2.191 2.45 44R-2, 33-34 547.44 2.914 2.836 2.731 2.06 44R-CC, 26-28 551.87 2.682 2.756 -2.697 2.10 45R-1,32-34 555.63 4.174 4.130 1.067 2.38 45R-2, 49-51 557.10 2.924 45R-2, 62-65 557.24 (1) 45R-CC, 19-21 561.96 2.758 2.748 0.358 2.13 46R-1,76-79 565.38 2.765 2.579 6.957 2.01 48R-1,40-44 584.32 2.455 48R-1,44-46 584.37 2.798 2.635 6.008 2.01 50R-1,2-5 603.24 2.629 2.546 3.173 2.15 5OR-3, 7-9 606.28 2.392 50R-3, 10-13 606.32 (1) 50R-5. 1-3 609.22 2.712 2.736 -0.881 2.14 50R-6, 126-128 611.97 2.610 2.338 10.975 2.03 51R-1.55-57 613.26 2.874 2.554 11.797 2.22 51R-3, 104-106 616.75 2.395 2.135 11.444 2.04 51R-4, 33-34 617.54 2.431 2.298 5.653 1.96 52R-1, 146-148 623.87 2.813 2.810 0.124 2.13 52R-2. 113-115 625.04 2.742 2.542 7.588 2.13 52R-3, 2-5 625.44 (1) 52R-3, 6-8 625.47 2.653 52R-4, 2^1 626.93 2.654 2.494 6.224 2.08 53R-3, 53-55 635.44 2.533 2.198 14.162 2.05 54R-1,91-93 642.72 3.647 3.794 -3.962 2.17 54R-1,93-96 642.75 3.690 54R-1,97-99 642.78 3.376 -8.888 54R-4, 32-36 646.32 4.182 54R-4, 36-38 646.34 4.019 3.916 2.574 2.25 54R-4, 39-41 646.37 4.542 8.253 54R-6, 108-110 650.06 4.780 5.498 -13.973 2.21 55R-2, 56-58 653.57 3.620 3.127 14.616 2.23 55R-3, 31-33 654.82 3.038 2.800 8.172 2.21 55R-3, 111-113 655.62 2.959 2.675 10.074 2.10 55R-5, 48-50 657.99 2.790 2.649 5.195 2.04 56R-1,79-81 662.00 2.815 2.585 8.513 2.08 56R-2, 113-115 663.84 2.644 56R-2, 115-117 663.86 4.053 3.648 10.536 2.03 56R-3, 68-70 664.89 2.703 56R-3, 70-72 664.91 4.174 4.841 -14.779 1.89 57R 1,31-33 671.02 2.917 2.448 17.506 2.03 57R-2, 131-133 673.52 3.021 2.845 5.974 2.04 57R3, 56-57 674.27 2.871 2.511 13.397 2.00 57R-CC, 16-19 675.37 3.299 3.040 8.188 2.23 58R-1,78-80 681.19 4.041 3.941 2.506 2.03 58R-5, 99-101 687.40 4.570 4.484 1.892 2.00 59R-1,56-58 690.57 2.684 2.501 7.049 1.94 59R-3, 7-9 693.08 2.766 2.526 9.056 2.03 59R-4, 2-A 694.53 2.861 2.764 3.469 2.05 59R-5, 8-10 696.09 3.153 2.891 8.654 2.04 59R-6, 57-60 698.09 3.527 59R-6, 61-63 698.12 3.362 -4.790 60R-2, 84-86 700.85 4.074 4.218 -3.481 2.09 60R-5, 81-83 705.32 3.225 3.192 1.027 2.15 60R-7, 122-124 708.73 3.048 3.009 1.269 2.12 60R-8, 20-22 709.21 2.573 2.381 7.760 1.92 61R-1,37-39 709.78 2.652 61R-1,39-44 709.81 (1) 61R-1,44-46 709.85 2.521 2.413 4.373 1.99 61R-2, 41-43 711.32 3.995 61R-2, 45-48 711.36 4.083 -2.179

345 SITE 869

Table 9 (continued).

Anisotropy Anisotropy Bulk Core, section. Depth V, (cu) V , (cu) V, (me) V, (me) (cu) (me) density interval (cm) (mbsf) (km/s) (km/s) (km/s) (km/s) (%) (%) (g/cm3)

61R-2, 48-50 711.39 4.254 3.947 7.491 2.09 63R-2, 48-50 730.69 3.025 2.503 18.890 2.10 63R-3, 28-31 732.00 2.563 63R-3, 74-76 732.45 2.703 2.481 8.564 1.95 63R-4, 78-80 733.99 2.765 2.811 -1.664 2.04 63R-4, 81-85 734.04 (1) 63R-6, 109-111 737.30 4.300 4.182 2.781 2.09 63R-CC, 2-4 738.34 4.412 63R-CC, 6-8 738.38 4.355 4.511 -3.530 2.16 64R-1, 112-114 739.53 3.069 3.141 -2.318 2.12 64R-2, 38-40 740.29 2.615 2.355 10.460 1.99 64R-3, 46-48 741.87 2.442 2.420 0.894 1.96 64R-3, 113-116 742.55 2.639 64R-4, 78-80 743.69 2.591 2.295 12.093 2.04 64R-5, 105-107 745.46 2.689 2.409 10.977 1.92 64R-6. 57-60 746.49 2.550 64R-6, 125-127 747.16 2.773 2.537 8.891 2.00 65R-1, 14-17 748.05 2.696 2.382 12.363 1.99 65R-1,70-73 748.62 2.426 65R-2, 115-117 750.56 2.807 2.364 17.102 2.04 65R-2, 123-125 750.64 2.674 2.264 16.600 1.96 65R-3. 14-16 751.05 2.798 2.476 12.223 2.04 65R-4, 3-7 752.45 2.335 65R-CC, 17-19 752.58 2.688 2.484 7.906 1.97 66R-1,2-4 757.63 2.833 2.683 5.442 2.04 66R-2, 2-4 759.13 3.283 3.302 -0.579 2.06 66R-3, 59-61 761.20 2.785 2.702 2.999 2.09 67R-1,74-76 768.05 2.778 2.587 7.094 2.04 67R-1, 146-149 768.78 2.375 67R-2. 72-74 769.53 2.725 2.666 2.201 2.20 67R-2, 96-98 769.77 2.567 2.397 6.825 1.90 67R-4, 40-42 772.21 2.812 2.336 18.479 2.02 67R-5, 91-93 774.22 2.596 2.323 11.083 1.93 67R-6, 50-52 775.31 2.725 2.439 11.061 1.96 67R-CC, 2-5 775.68 68R-1,58-60 777.49 2.655 2.371 11.287 1.95 68R-1,60-63 777.53 1.951 68R-2, 44-47 778.88 2.575 68R-2, 48-50 778.89 2.726 2.577 5.604 2.03 68R-3, 53-57 780.45 2.686 68R-4, 57-59 781.98 3.463 3.161 9.113 2.36 68R-3, 67-69 780.58 2.751 2.422 12.738 2.02 68R-5, 58-60 783.49 3.009 2.478 19.343 2.06 69R-1,7-9 786.68 4.196 4.009 4.547 2.35 69R-1, 144-146 788.05 2.768 2.353 16.201 2.04 69R-2, 21-23 787.94 2.693 2.365 12.986 2.09

Note: Measurements are labeled for direction and sample shape: V (cu) is transverse (horizontal) from a cube; V/;/(cu) is longitudinal (parallel core-axis) from a cube; V;,,(mc) is transverse from a minicore; V^mc) is longitudinal from a minicore. Samples that were too long for acoustic measurements (minicores) or collapsed during measurement have been labeled (1) and (2), respectively.

Core 143-869A-15X, from 135.5 to 145.5 mbsf, but in this core, only No prominent reflector marks the unconformable contact between a trace of porcellanite is seen. Nonetheless, drilling rates slowed Paleocene cherty radiolarian ooze above and late Campanian-early markedly in the last few meters of coring, and chert fragments were Maastrichtian volcaniclastic sandstone, siltstone, and claystone be- recovered in the following core (143-869A-16X). We suppose that the low, which is at a depth of about 207 mbsf in the cores, based on the chert was present in the lowest few meters of the upper coring interval, depth to Sample 143-869B-8R-CC, where the first Cretaceous nanno- but was not recovered. The interval velocity, to Reflector Cl (at fossils were noted. A break occurs in the sonic, density, and resistivity 70 mbsf), is 1.78 km/s. The age of Reflector C2 is early Eocene. logs at 207 mbsf, with generally smaller values below this depth, but Reflector C2 also has an irregular, hummocky surface with a relief the change is too small to generate a sufficient impedance contrast to of about 10 m, which may be caused by diagenetic effects that produce produce a reflector, and nothing can be seen in the seismic profile at chert at variable stratigraphic levels. the appropriate two-way reflection time (about 0.23 s). Reflector C3, at about 0.190 s twtt bsf, was assigned to the major Reflector Kl is the top of a bundle of reflectors, from about 0.345 change in lithology at 165 mbsf, as shown in the downhole logs of to 0.390 s twtt bsf. It most plausibly corresponds to the group of hole diameter, resistivity, sonic velocity, and density. The lower volcaniclastic sandstones in Cores 143-869B-19R to -21R, from Eocene and upper Paleocene radiolarian-nannofossil oozes below this about 303 to 331 mbsf, in the lower Campanian sequence. level, to a depth of about 207 mbsf, contain chert nodules; in fact, the Reflector K2 is the top of an interval of radiolarian claystone and poorly recovered section in the interval from 165 to 207 mbsf consists siltstone of early Campanian age from 378 to 394 mbsf. The increases of mainly chert fragments. in velocity, density, and resistivity seen in the downhole logs probably

346 SITE 869

Table 10. Measurements from the digital sound velocimeter for Site 869. Table 11. Thermal conductivity data for Site 869.

Core, section, Depth Velocity Core, section, Depth Velocity Thermal Thermal interval (cm) (mbsf) (km/s) interval (cm) (mbsf) (km/s) Core, section, Depth conductivity Core, section, Depth conductivity interval (cm) (mbsf) (W/[m • K]) interval (cm) (mbsf) (W/[m • K]) 143-869 A- 8H-6, 84 73.59 .545 8H-7, 84 75.09 .532 143-869 A- 9H-5, 75 82.95 1.197 1H-1, 123 1.23 .493 8H-8, 68 76.43 .555 9H-6, 75 84.45 0.910 lH-1,75 0.75 .482 9H-1,75 76.95 .550 3H-1, 100 20.20 1.011 10X-2, 55 87.75 1.093 1H-2, 86 2.36 .463 9H-2, 75 78.45 .530 3H-2, 100 21.70 0.911 11X-3, 75 99.25 1.105 lH-3,72 3.72 .469 9H-3, 75 79.95 .517 3H-3, 100 23.20 1.036 11X-1.75 96.25 0.796 1H-4, 72 5.22 .491 9H-4, 75 81.45 .533 3H-4, 100 24.70 0.741 11X-5, 53 102.03 0.852 1H-5.72 6.72 .504 9H-5, 102 83.22 .523 3H-5, 75 25.95 1.094 11X-4, 75 100.75 0.996 1H-6, 72 8.22 .488 9H-6, 75 84.45 .520 3H-6, 75 27.45 0.900 12X-1.75 106.25 0.849 lH-7,30 9.30 .496 9H-7, 27 85.47 .528 3H-1, 100 20.20 0.970 12X-2, 75 107.75 0.886 2H-L75 10.45 .471 1OX-1,38 86.08 .530 4H-1,75 29.45 1.727 12X-3, 75 109.25 1.081 2H-2, 75 11.95 .510 10X-2, 67 87.87 .527 4H-2, 75 30.95 1.386 12X-4, 75 110.75 0.789 2H-3, 75 13.45 .514 11X-1, 107 96.57 .555 4H-3, 75 32.45 1.233 12X-5, 57 112.07 1.001 2H-4, 75 14.95 .502 11X-2, 80 97.80 .543 4H-4, 75 33.95 0.928 13X-1, 75 116.25 0.807 2H-5, 75 16.45 .506 11X-3, 79 99.29 .547 4H-5, 75 35.45 0.872 13X-2, 75 117.75 0.916 2H-6, 75 17.95 .465 11X-4, 35 100.35 .533 4H-6, 75 36.95 1.215 13X-3, 84 119.34 0.784 2H-7, 24 18.94 .502 11X-5, 27 101.77 .550 4H-7, 25 37.95 1.192 13X-4, 49 120.49 0.820 3H-1, 105 20.25 .466 12X-1.60 106.10 .528 5H-1,75 38.95 1.165 13X-5, 29 121.29 0.747 3H-2, 98 21.68 .465 12X-2, 99 107.99 .540 5H-2, 75 40.45 0.904 14X-2, 75 127.75 0.803 3H-3, 49 22.69 :.501 12X-2, 69 107.69 .499 5H-3, 75 41.95 1.321 14X-3, 75 129.25 0.889 3H-4, 75 24.45 .479 12X-3, 75 109.25 .528 5H-4, 75 43.45 1.247 14X-4, 68 130.68 0.753

3H-4, 87 24.57 .476 12X-4, 68 110.68 • .560 5H-5, 75 44.95 0.869 14X-5, 50 132.00 0.829

3H-6, 75 27.45 .482 12X-4, 102 111.02 : .515 5H-6, 75 46.45 .367 14X-6, 30 132.80 0.851

4H-1.75 29.45 .504 12X-5, 56 112.06 : .543 6H-1.75 48.45 .086 15X-1, 75 136.25 0.718 4H-2, 75 30.95 .504 13X-2, 101 118.01 .554 6H-2, 75 49.95 .305 15X-2, 54 137.54 0.802 4H-3. 58 32.28 .502 13X-2, 20 117.20 .560 6H-3, 75 51.45 .030 15X-3, 75 139.25 0.918 4H-3, 114 32.84 .514 13X-3, 74 119.24 .560 6H-4, 75 52.95 .162 15X-4, 78 140.78 0.867

4H-4, 123 34.43 .509 13X-3,50 119.00 : .560 6H-5, 75 54.45 .296 15X-5, 76 142.26 0.789

4H-5, 75 35.45 .462 13X-4, 15 120.15 : .555 6H-6, 75 55.95 ().799 15X-6, 39 143.39 0.851 4H-6, 60 36.80 : .520 13X-4, 53 120.53 .547 6H-7, 25 56.95 .410 4H-7, 25 37.95 .515 13X-5, 25 121.25 .542 7H-2, 75 58.07 .347 143-869B- 5H-1.75 38.95 .522 14X-2, 42 127.42 .554 7H-3, 75 59.57 .510 5H-2, 75 40.45 .477 14X-3, 86 129.36 .522 7H-4, 75 61.07 ().937 16R-1.50 275.60 1.235 5H-3, 75 41.95 .444 14X-3, 40 128.90 .559 7H-5, 75 62.57 .331 15R-1.73 266.13 0.955 5H-4, 75 43.45 .528 14X-4, 99 130.99 .564 7H-6, 75 64.07 .225 15R-2, 62 267.52 1.077 5H-5, 75 44.95 .537 14X-5, 43 131.93 .522 7H-7, 75 65.57 .136 15R-3,72 269.12 0.994 5H-6, 75 46.45 .532 14X-5, 24 131.74 .560 7H-8, 25 66.57 .213 15R-4, 75 270.65 1.150 5H-7, 25 47.45 .520 14X-6, 15 132.65 .462 8H-2, 75 67.50 .494 15R-5, 26 271.66 1.020 6H-1,75 48.45 .522 15X-1,84 136.34 .554 8H-3, 75 69.00 .415 10R-l,60 217.80 1.230 6H-2. 75 49.95 .514 15X-1, 50 136.00 .566 8H-4, 75 70.50 .307 10R-1, 122 218.42 1.151 6H-3, 75 51.45 .520 15X-2, 67 137.67 .557 8H-5, 75 72.00 .435 10R-2, 40 219.10 1.305 6H-4. 75 52.95 .535 15X-2, 39 137.39 .562 8H-6, 75 73.50 .459 11R-1,75 227.65 0.918 6H-5, 86 54.56 .530 15X-3, 97 139.47 .507 8H-7, 75 75.00 .363 11R-2, 75 229.15 1.034 6H-6, 75 55.95 .540 15X-3, 79 139.29 .506 8H-8, 40 76.15 .164 11R-3, 70 230.60 1.288 6H-7, 28 56.98 .520 15X-3,39 138.89 .571 9H-1.75 76.95 .404 11R-4, 82 232.22 1.334 7H-2, 75 58.07 .523 15X-4, 56 140.56 .401 9H-2, 75 78.45 .406 13R-1,44 246.64 1.016 7H-2, 39 57.71 .535 15X-4, 130 141.30 .566 9H-3, 75 79.95 .276 13R-2, 76 248.46 1.272 7H-3, 75 59.57 .525 15X-5, 94 142.44 .576 9H-7, 40 85.60 .074 13R-3, 70 249.90 1.232 7H-4, 75 61.07 .525 15X-6, 33 143.33 .580 9H-4, 75 81.45 0.953 13R-4, 56 251.26 1.340 7H 5 75 62 57 562 7H-6, 75 64.07 .559 143-869B- 7H-7, 75 65.57 .545 7H-8, 42 66.74 .567 10R-l,95 218.15 1.639 8H-2, 75 67.50 .566 lOR-2,44 219.14 1.376 the unit, marked by Reflector K6 (0.640 s twtt) at 654 mbsf, and a 8H-3, 75 69.00 .535 11R-1,89 227.79 1.576 more gradational change in properties at the top of the interval. An 8H-4, 84 70.59 .562 1IR-2, 76 229.16 0.641 extremely strong peak in the gamma-ray log, most plausibly associ- 8H-5, 84 72.09 .554 143-869B-51R, lies immediately above the upper debris flows in the were caused by extensive diagenesis of these relatively siliceous sequence. The geochemical log shows this to be high in potassium strata. The impedance change at the base of this interval, at 378 mbsf, and thorium and thus is most likely an ashy layer. has been selected as Reflector K2A, at 0.440 s twtt. Between 654 mbsf and the total depth of Hole 869B, the strata Reflector K3 is the top of a 25-m-thick set of massive coarse debris consist of sandy turbidites, each with a "Christmas-tree" profile in the flows and turbidites from about 509 to 543 mbsf, in Cores 143-869B- downhole logs, and these probably make up the series of closely 40R to -43R in the upper Cenomanian. All the downhole sonic, spaced weak reflectors in the seismic profile, below 0.640 s twtt. No resistivity, density, and caliper logs show this lithologic unit which has readily apparent base is seen for the reflectors, that is, no strong a moderately strong impedance contrast at the top (which is a somewhat "acoustic basement." The last visible reflector in this profile (Reflec- gradational contact) and a very strong (negative) impedance contrast tor K7) is seen at about 0.89 s twtt. An even deeper, very faint reflector at the base (which is marked in the seismic profile by Reflector K4). at 1.05 s twtt was noted in the JOIDES Resolution profile, which was Reflector K5, at 0.620 s twtt, was selected at 617 mbsf, at the top shot with a larger acoustic source (Fig. 9). This suggests that the of a series of upper Cenomanian debris flows and sandy turbidites seismic reflection penetration at Site 869 was limited by the profiling that begins at 654 mbsf in the upper part of Section 2 of Core equipment and that true volcanic basement may be very deep. 143-869B-55R. The downhole logs show a typical "Christmas-tree" A plot of two-way reflection times vs. depth in Hole 869B is given profile, with a very large negative impedance contrast at the base of in Table 12, and the values are plotted in Figure 57. In this figure, the

347 SITE 869 extrapolated depth to Reflector K7 is shown as 1000 mbsf, if allow- Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton ance were made for further increases downward in interval sonic zonation. In Farinacci, A. (Ed.), Proc. 2nd Int. Conf. Planktonic Microfos- velocity. A straight-line extrapolation, having the same velocity cal- sils Roma: Rome (Ed. Tecnosci.), 2:739-785. culated for the interval between Reflectors K5 and K3, gives an McNutt, M.K., and Fischer, K.M., 1987. The South Pacific superswell. In estimated depth of about 950 mbsf for Reflector K7. Reflector K8, at Keating, B.H., Fryer, P., Batiza, R., and Boehlert, G.W. (Eds.), Sea- mounts, Islands, and Atolls. Am. Geophys. Union, Geophys. Monogr. 1.05 s twtt, has been estimated to be at about 1230 mbsf. Ser., 43:25-34. Moberly, R., Schlanger, S.O., and Shipboard Scientific Party, 1986. Site 585. REFERENCES* In Moberly, R., Schlanger, S.O., et al., Init. Repts., DSDP, 89: Washington (U.S. Govt. Printing Office), 29-156. Berger, W.H., Vincent, E., and Thierstein, H.R., 1981. The deep-sea record: Mutti, E., and Ricci Lucchi, F., 1972. Le torbiditi del 1' Appennino settentrional: major steps in Cenozoic ocean evolution. In Warme, J.E., Douglas, R.G., introduzione alFanalisi de facies. Mem. Soc. Geol. Itai, 11:161-199. and Winterer, E.L. (Eds.), The Deep Sea Drilling Project: A Decade of Nakanishi, M., Tamaki, K., and Kobayashi, K., 1992. Magnetic anomaly Progress. Spec. Publ.—Soc. Econ. Paleontol. Mineral., 32:489-504. lineations from Late Jurassic to Early Cretaceous in the west-central Berger, W.H., and Winterer, E.L., 1974. Plate stratigraphy and the fluctuating Pacific Ocean. Geophys. J. Int., 109:701-719. carbonate line. In Hsü, K.J., and Jenkyns, H.C. (Eds.), Pelagic Sediments Normark, W.R., 1970. Growth patterns of deep-sea fans. AAPG Bull., on Land and Under the Sea. Spec. Publ. Int. Assoc. Sedimentol., 1:11—48. 54:2170-2195. Berggren, W.A., Kent, D.V., Flynn, J.J., and Van Couvering, J.A., 1985. Perch-Nielsen, K., 1985. Mesozoic calcareous nannofossils. In Bolli, H.M., Cenozoic geochronology. Geol. Soc. Am. Bull, 96:1407-1418. Saunders, J.B., and Perch-Nielsen, K. (Eds.), Stratigraphy: Cole, W.S., 1954. Larger and smaller diagnostic foraminifera Cambridge (Cambridge Univ. Press), 329-426. from Bikini drill holes. U.S. Geol. Sum Prof. Pap., 260-V: Washington Petersen, L.D., Duennebier, F.K., and Shipley, T.H., 1986. Site surveys in the (U.S. Govt. Printing Office), 743-784. western Pacific conducted aboard the Kana Keoki, Cruise KK810626 Davis, A.S., Pringle, M.S., Pickthom, L.B.G., Clague, D.A., and Schwab, Leg 4. In Moberly, R., Schlanger, S.O., et al., Init. Repts. DSDP, 89: W.C., 1989. Petrology and age of alkalic lava from the Ratak chain of the Washington (U.S. Govt. Printing Office), 311-319. Marshall Islands. J. Geophys. Res., 94:5757-5774. Pickering, K.T., Hiscott, R.N., and Hein, F.J., 1989. Deep Marine Environ- Duncan, R.A., and Clague, D.A., 1985. Pacific plate motions recorded by ments: Clastic Sedimentation and Tectonics: London (Unwin Hyman). linear volcanic chains. In Nairn, A.E.M., Stehli, F.G., and Uyeda, S. (Eds.), Premoli Silva, I., andBrusa, C. 1981. Shallow-water skeletal debris and larger The Ocean Basins and Margins (Vol. 7A): The Pacific Ocean: New York foraminifers from Deep Sea Drilling Project Site 462, Nauru Basin, (Plenum), 89-121. western equatorial Pacific. In Larson, R.L., Schlanger, S.O., et al., Init. Emery, K.O.. Tracey, J.I., Jr., and Ladd, H.S., 1954. Geology of Bikini and Repts. DSDP, 61: Washington (U.S. Govt. Printing Office), 439^73. Nearby Atolls. U.S. Geol. Surv. Prof. Pap., 260-A: 1-265. Pringle, M.S., Jr., 1992. Geochronology and petrology of the Musicians Fischer, A.G., 1986. Climatic rhythms recorded in strata. Annu. Rev. Earth Seamounts, and the search for hot spot volcanism in the Cretaceous Pacific Planet. Sci., 14:351-376. [Ph.D. dissert.]. Univ. of Hawaii, Honolulu. Haggerty, J.A., and Premoli-Silva, I., 1986. Ooids and shallow-water debris Rea, D.K., and Valuer, T.L., 1983. Two Cretaceous volcanic episodes in the in Aptian-Albian sediments from the East Mariana Basin, Deep Sea western Pacific Ocean. Geol. Soc. Am. Bull., 94:1430-1437. Drilling Project Site 585: implications for the environment of formation of Sager, W.W., 1986. Magnetic-susceptibility measurements of metal contaminants ooids. In Moberly, R., Schlanger, S.O., et al., but. Repts DSDP, 89: in ODP Leg 101 cores. In Austin, J.A., Jr., Schlager, W., et al., Proc. ODP, Washington (U.S. Govt. Printing Office), 399-412. Init. Repts., 101: College Station, TX (Ocean Drilling Program), 39^6. Hambach, U., and Krumsiek, K., 1989. A magnetostratigraphic subdivision of , 1988. Paleomagnetism of Ocean Drilling Program Leg 101 sedi- the upper Albian and lower Cenomanian on the basis of drill cores from ments: magnetostratigraphy, magnetic diagenesis, and paleolatitudes. In wells in the Ruhr area. Geol. Jahrb., Al 13:401^25. Austin, J.A., Jr., Schlager, W., etal., Proc. ODP, Sci. Results, 101: College Hamilton, E.L., and Rex, R.W., 1959. Lower Eocene Phosphatized Globigerina Station, TX (Ocean Drilling Program), 327-360. Ooze from Sylvania Guyot. U.S. Geol. Surv. Prof. Pap., 260-W:785-797. Schlager, W., 1980. Mesozoic calciturbidites in Deep Sea Drilling Project Hancock, J.M., and Kauffman, E.G., 1979. The great trangressions of the Late Hole 416A: recognition of a drowned carbonate platform. In Lancelot, Y., Cretaceous. J. Geol. Soc. London, 136:175-186. Winterer, E.L., et al., Init. Repts. DSDP, 50: Washington (U.S. Govt. Jenkyns, H.C, 1972. Pelagic "oolites" from the Tethyan Jurassic. J. Geol., Printing Office), 733-749. 80:21-33. Schlanger, S.O., 1963. Subsurface geology of Eniwetok Atoll. U.S. Geol. Surv. Jenkyns, H.C, and Schlanger, S.O., 1981. Significance of plant remains in Prof. Pap., 260-BB:991-1066. redeposited Aptian sediments, Hole 462A, Nauru Basin, to Cretaceous , 1986. High frequency sea-level fluctuations in Cretaceous time: an oceanic-oxygenation models. In Larson, R.L., and Schlanger, S.O., et al., emerging geophysical problem. In Hsü, K.J. (Ed.), Mesozoic and Cenozoic Init. Repts. DSDP, 61: Washington (U.S. Govt. Printing Office), 557-562. Oceans. Am. Geophys. Union, 61-74. Kent, D.V., and Gradstein, F.M., 1985. ACretaceous and Jurassic geochronol- Schlanger. S.O., Arthur, M.A., Jenkyns, H.C, and Scholle, P.A., 1987. The ogy. Geol. Soc. Am. Bull., 96:1419-1427. Cenomanian-Turonian Oceanic Anoxic Event, I. Stratigraphy and distri- Kulp, L.J., 1963. Potassium-argon dating of volcanic rocks. Bull. Volcanol., bution of organic carbon-rich beds and the marine δ C excursion. In 26:247-258. Brooks, J., and Fleet, A.J., Marine Petroleum Source Rocks. Geol. Soc. Larson, R.L., 1976. Late Jurassic and Early Cretaceous evolution of the London Spec. Publ., 26:371-399. western Central Pacific Ocean. /. Geomagn. Geoelectr., 28:219-236. Schlanger, S.O., Jenkyns, H.C, and Premoli Silva, I., 1981. Volcanism and Larson, R.L., and Schlanger, S.O., 1981. Geological evolution of the Nauru vertical tectonics in the Pacific Basin related to global Cretaceous trans- Basin, and regional implications. In Larson, R.L., Schlanger, S.O., et al., gressions. Earth Planet. Sci. Lett., 52:435-449. Init. Repts DSDP, 61: Washington (U.S. Govt. Printing Office), 841-862. Schlanger, S.O., and Premoli Silva, I., 1981. Tectonic, volcanic, and paleo- Lincoln, J.M., Pringle, M.S., and Premoli Silva, I., in press. Early and Late geographic implications of redeposited reef faunas of Late Cretaceous and Cretaceous volcanism and reef-building in the Marshall Islands. In Pringle. Tertiary age from the Nauru Basin and the Line Islands. In Larson, R.L., M.S., Sager, W.W., Sliter, W. V, and Stein, S. (Eds.), The Mesozoic Pacific. Schlanger, S.O., et al., Init. Repts. DSDP, 61: Washington (U.S. Govt. Am. Geophys. Union, Geophys. Monogr. Ser. Printing Office), 817-827. Lisitzin, A.P., 1971. Distribution of siliceous microfossils in suspension and , 1986. Oligocene sea-level fall recorded in mid-Pacific atoll and bottom sediments. In Funnell, B. M., and Riedel, W. R. (Eds.), The Micropa- archipelagic apron settings. Geology, 14:392-395. laeontology of the Oceans: Cambridge (Cambridge Univ. Press), 173-195. Sissingh, W., 1977. Biostratigraphy of Cretaceous calcareous nannoplankton. Geol. Mijnbouw, 56:37-65. Tarduno, J.A., Lowrie, W., Sliter, W.V., Bralower, T.J., and Heller, F, 1992. * Abbreviations for names of organizations and publication titles in ODP Reversed polarity characteristic magnetizations in the Albian Contessa reference lists follow the style given in Chemical Abstracts Service Source section, Umbrian Apennines, Italy: implications for the existence of a Index (published by American Chemical Society). mid-Cretaceous mixed polarity interval. J. Geophys. Res., 97:241-271. SITE 869

Tarduno, J.A., Mayer, L.A., Musgrave, R., and Shipboard Scientific Party, 1991. Warme, J.E., Kennedy, W.J., and Schneidermann, N., 1973. Biogenic sedimentary High-resolution, whole-core magnetic susceptibility data from Leg 130, structures (trace fossils) in Leg 15 cores. In Edgar, N.T., Saunders, J.B., et al., Ontong Java Plateau. In Kroenke, L.W., Berger, W.H., Janecek, T.R., et al., Init. Repts. DSDP, 15: Washington (U.S. Govt. Printing Office), 813-831. Pwc. ODP, Init. Repts., 130: College Station, TX (Ocean Drilling Pro- Wetzel, A., 1991. Ecologic interpretation of deep-sea trace fossil communities. gram), 541-548. Palaeogeogr., Palaeoclimatol, Palaeoecoi, 85:47-69. Tarduno, J.A., Sliter, W.V., Bralower, T.J., McWilliams, M., Premoli Silva, I., and Ogg, J.G., 1989. M-sequence reversals recorded in DSDP sediment cores from the western Mid-Pacific Mountains and Magellan Rise. Geol. Soc. Am. Bull., 101:1306-1316. van Andel, T.H., 1975. Mesozoic-Cenozoic calcite compensation depth and the global distribution of calcareous sediments. Earth Planer. Sci. Lett., 26:187-194. Ms 143IR-109

NOTE: For all sites drilled, core-description forms ("barrel sheets") and core photographs have been reproduced on coated paper and can be found in Section 3, beginning on page 381. Forms containing smear-slide data can be found in Section 4, beginning on page 691. Conventional and geochemical-log, FMS, and dipmeter data can be found in CD-ROM form (back pocket).

Bulk density (g/cm3) Porosity (%) Water content (%) Grain density (g/cm3) Velocity (km/s) GRAPE density (g/cm3) 1.1 1.6 2.1 2.6 0 25 50 75 100 0 20 40 60 80100 2 2.5 3 12 3 4 5 6 1.1 1.6 2.1 2.6 1 ' ' ' o ' ç 0° c °o + DSV - o Discrete

0° 8 o 100 o o

o O - o o o - A 0 o o 1 0 c 200

0

- o - f q3 c5 *boα> 0 o co α> 300 © O CD CDg eε> o° 0 o - o - <§> oo o 0 400 0 O o <öo Θ COo O CO oo O CD - oo oó> 0 no o θ cö O o 500 o o - fo - <δ - COCO

So e

0 600 - -

c§ o o 0 ' 0 © 700 - O (ß Oo w, o1 c I I I ! I I 1 1 1 1 800

Figure 44. Index properties, sonic velocity, and GRAPE-density data for Holes 869A and 869B.

349 SITE 869

Bulk density (g/cm3) Velocity (km/s) Velocity (km/s) (DSV) (P-wave logger) 1.0 1.5 2.0 1.4 1.5 1.6 1.7 1.4 1.5 1.6 1.7 0

50

-Q E

Q. CD Q

100

GRAPE * Discrete ° 150 I I Figure 45. Bulk density from discrete measurements and GRAPE-density logger, and P-wave velocity from the DSV and MST P-wave logger, vs. depth, Hole 869A. SITE 869

Velocity (km/s) Anisotropy (%) Bulk density (g/cm) Recovery (%) Log 12 3 4 5 6-30-15 0 15 30 1.1 1.6 2.1 2.6 0 20 40 60 80100 units P?'' 1a

80

100 1b ^' 145 • o o o 1c 200 210

+ DSV 0 Vp, (cu) o 0 300 Vp/ (cu) Δ T *' Vp, (me) o %° Δ I t Vp/ (me) o . t l I O I „ o°o -QD- 377 400 3a çpo 425 If oo o o o<5> 3b 500 β α o 534

600

639

5a 700 720

'£.*. 5b 800 S Figure 46. Plot of sonic velocity, anisotropy, bulk density, and recovery for Site 869. Indicated on the left are the physical property units (depth in mbsf). DSV = digital sound velocimeter; Vpt is transverse; Vpl is longitudinal (parallel core-axis); letters in parentheses in legend indicate measurements from cubes, "cu," or measurements from minicores, "me."

351 Site 869

E~ Total gamma (API) Velocity (km/s) Velocity (km/s) Density (g/cm3) Density (g/cm3) Resistivity (ohm m) Recovery (%) (from log) (from log) (from log) (from log) 0 20 40 0 2 4 6 2 4 6 1.1 1.6 2.1 2.6 1.1 1.6 2.1 2.6 0 2 4 6 8 0 40 80

"-*• -'-Radiolarian nannofossil ooze

100 - Radiolarian-nannofossil ooze and nannofossil- radiolarian ooze with porcellanites and chert 200

Volcaniclastic sandstone to silstone with nannofossil- 300 rich claystone intervals interbedded with local calcareous-rich levels

400 " Radiolarian claystone to siltstone and volcaniclastic _ _ _sandstone _ _ _ _As_for_subunit IjJA 500 Volcaniclastic breccia Volcaniclastic sandstone and breccia interbedded with 600 - radiolarian claystone and clayey nannofossil chalk

Volcaniclastic sandstone- 700 - siltstone with rare nannofossil- rich siltstone and radiolarian- rich layers

800 -1 Volcaniclastic siltstone and calcareous claystone with radiolarians

Figure 47. Comparison of lithostratigraphy with index physical properties, sonic velocity and density, and wireline log measurements (gamma, sonic velocity, density, and resistivity) for Site 869. SITE 869

Shallow resistivity (ohm-m) 0.2 2000

100 -

200 -

300 -

400 -

500 ~

600 ~

700 -

800 Figure 48. Summary of logs used to define logging units, Hole 869B. Unit boundaries are shown within the SGR (total gamma) and SFLU (shallow- resistivity) data columns. RHOB is density and NPHI is porosity. The mechani- cal caliper log is on the right.

353 SITE 869

SFLU (ohm-m) 0.2 2000

100

200

300

400 -

a. CD Q

500

600

700 -

800

Figure 49. Comparison of velocity and resistivity logs, Hole 869B. SITE 869

SGR Uranium Thorium Potassium (API units) (ppm) (ppm) (wt%) 0 250 -5 20 30 -0.01 0.07 350 i i i i i r \ i i i i i i

400

450

500

550 >

600 i i i i i i i i i i i i i i i i

Figure 50. Spectral gamma-ray log compared with uranium, thorium, and potassium logs, Hole 869B.

355 SITE 869

SGR Silicon Iron Sulfur Aluminum (API units) 0 250 0.0 0.35 -0.05 0.2 -0.02 0.05 -0.02 0.12 350 1 II I l II

400

450

CL a

500

550

600 I I l l I I I I I I I I I I I I I I

Figure 51. Spectral gamma-ray log compared with relative yield of silicon, iron, sulfur, and aluminum, expressed as decimal fractions. Calcium was uniformly zero for the entire logged interval.

356 SITE 869

Horizontal (nT) Orientation (degrees) 10000 30000 90 180 270 200

800

Figure 52. Variations of horizontal and vertical components of the geomagnetic field, and the orientation of the tool with respect to the present geomagnetic field within Hole 869B from 239 to 725 mbsf. Dashed lines indicate the boundaries of the log-based units. Arrows show the normal- reverse polarity boundaries inferred from vertical magnetic field variations and shipboard paleo- magnetic results. K-N indicates the Cretaceous normal super chron.

357 SITE 869

Resistivity (ohm-m) Shallow-F resistivity Shallow-F resistivity 1 10 100 1000 1 10 100 1000 1 10 100 1000 350 480 Medium resistivity Shallow resistivity Deep resistivity

355

I 360

365

370 Figure 54. Shallow resistivity profiles of large fining-upward sequences bound- Figure 53. Comparison of deep-, medium-, and shallow-focused resistivity ing logging Unit 5 (left) 487.2 to 534.0 mbsf (Cores 143-869B-38R through measurements, Hole 869B. -42R), (right) 625.8 to 654.2 mbsf (Cores 143-869B-52R through Section 143-869B-55R-2).

cm 24-1

26"

28-

30 -1 Figure 55. Interval 143-869B-55R-2, 24-30 cm, close-up photo showing contact between the breccias of the second fining-upward sequence and the underlying siltstones. (Same close-up photo as Figure 25.) SITE 869

Site 869

2000 UTC 2030 2100

Seafloor Reflector

0.085 s (C1)

0.165 (C2) 0.190 (C3)

0.345 (K1)

0.420 (K2) 0.440 (K2A)

0.530 (K3) 0.550 (K4)

0.620 (K5) 0.640 (K6)

0.890 (K7)

Figure 56. Seismic reflection profile at Site 869, showing two-way reflection time to most prominent reflectors. Profile taken by the Thomas Washington of the Scripps Institution of Oceanography, during Leg 8 of the Tunes Expedition. SITE 869 Two-way traveltime (s) 0.4 0.6 0.8 Table 12. Prominent reflectors seen in Figure 56, showing their corresponding depths in Holes 869A and 869B.

Twtt Ave. vel. Reflector (bsf) Depth Int. vel. to seafloor no. (s) (mbsO (km/s) (km/s)

Cl 0.085 70 1.65 1.65 C2 0.165 141 1.78 1.71 C3 0.19 165 1.92 1.74 Kl 0.345 303 1.78 1.76 K2 0.42 378 2.00 1.80 K2A 0.44 394 1.79 K3 0.53 509 2.38 1.92 K4 0.55 534 1.94 K5 0.62 617 2.40 1.98 K6 0.64 654 2.04 K7 0.89 1000 2.77 2.24 KK 1.05 1230 2.86 2.34

Interval velocities between reflectors and average velocities to the seafloor are shown in the last two columns of the 1400 table. Figures in italics are estimated values from Figure 57. Plot of depth in Hole 869B vs. reflection time of the most prominent extrapolation of the curve in Figure 57. reflectors shown in Figure 56. The final two points, at 1000 and 1230 mbsf, have been extrapolated from the curve where control is good. SITE 869

Hole 869B: Resistivity-Sonic-Natural Gamma Ray Log Summary

SPECTRAL GAMMA RAY RESISTIVITY TOTAL FOCUSED API units 80 1.2 2000 O "~ I COMPUTED MEDIUM II API units 80 1.2 ohm m 2000 LU O cog CALIPER DEEP VELOCITY I -J in 19 1.2 ohm m 2000 I 1.5 km/s

50- -50

DRILL PIPE OPEN HOLE

100- -100

150- -150

361 SITE 869

Hole 869B: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY RESISTIVITY TOTAL FOCUSED | o API units 2000

Q r | COMPUTED MEDIUM, SX lo API units 80 1.2 ohm m 2000 CALIPER DEEP VELOCITY I É 19 1.2 ohm m 2000 I 1.5 km/s ~π LU LU 5 Q CΛ

200- -200

250- -250

300- -300 SITE 869

Hole 869B: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY RESISTIVITY TOTAL FOCUSED API units 2000 .COMPUTED I ..MEDIUM. if API units 80 1.2 ohm m 2000 1 S CALIPER I DEEP VELOCITY En! in 19 1.2 ohm m 2000 I 1.5 km/s Q- < S8

350- -350

400- -400

450- -450

500- -500

363 SITE 869

Hole 869B: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY RESISTIVITY TOTAL FOCUSED API units 2000

Q r I COMPUTED MEDIUM, API units 80 1.2 ohm m 2000 &8 CALIPER I DEEP VELOCITY Eα! 19 1.2 ohm m 2000 I 1.5 km/s

550- -550

600- -600

650- -650

364 SITE 869

Hole 869B: Resistivity-Sonic-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY RESISTIVITY TOTAL FOCUSED API units go | .2 20CX) Q r I dPUTED ..MEDIUM., 08 I' API units βO 1.2 ohm m 2000

En! CALIPER DEEP VELOCITY Q- < D. < UJ UJ 9 in 19 .2 ohm m 2000 1.5 km/s 5

700- -700

750- -750

800- -800

850- 850

365 SITE 869

Hole 869B: Density-Porosity-Natural Gamma Ray Log Summary

SPECTRAL GAMMA RAY TOTAL I I POTASSIUM I 0 API units ^| 1-0.5 wt. % Zs\ 5 f PHOTOELECTRIC 5 C O~ I COMPUTED [...NEUTRON POROSIJY_ I EFFECT I .THORIUM I O ~ m§ lo API units 80 1100 PP™ olo barns/β" 101 -3 PPm 7 1 mg x —1 1 —1 £< I CALIPER I BULK DENSITY I DENSITY CORRECTION I URANIUM I £< Q CΛ I9 in 19 11 g/cm3 31 -0.25 9/cm3o.2519 PPm -1I Q w

0 1^ I I I I I I >i I I I 1 I I I I I n I I / I ° > \ )

~*" "^ ] f

50- '\ ' ) -50 -ft :' y ? { \

> / / / -•'j|^;* J ^ 1 i DRILL PIPE 1 V --— *££ ,.-"-v ^ V \θPENHOLE\

100- C >'^*.b "f ^" ? { ] "10°

150-^ »•^^j i V. I / ) "150

366 SITE 869

Hole 869B: Density-Porosity-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY TOTAL POTASSIUM API units 80 -0.5 wt. % 4.5 PHOTOELECTRIC COMPUTED NEUTRON POROSITY EFFECT THORIUM II m m 0 API units 801100 PP olo barns/β" 10 I-3 PP M x —i CALIPER I BULK DENSITY | DENSITY CORRECTION I URANIUM g 3 in 19 11 g/cm 3 I -0.25 9/cm3 0.25 I 9 ppm

200- -200

<

250- -250

300^ -300

367 SITE 869

Hole 869B: Density-Porosity-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY TOTAL POTASSIUM API units -0.5 wt. % 4.5 PHOTOELECTRIC if COMPUTED [...NEUTRON POROSfTY...I . EFFECT THORIUM m CD Q API units 80 1100 PP olo barns/e 10 I-3 ppm 7 CALIPER BULK DENSITY DENSITY CORRECTION URANIUM 3 3 9 in 19 1 g/cm 3 -0.25 0/cm 0_25 9 ppm -1

X.. 350- -350

•'v

400- -400

'J

>

( 450- -450 <

c

500- -500 SITE 869

Hole 869B: Density-Porosity-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY TOTAL POTASSIUM API units 80 -0.5 wt. % 4.5 PHOTOELECTRIC II COMPUTED NEUTRON POROSITY EFFECT THORIUM 81 t rr m 8 10 API units 801100 PPm o 10 barns/e- 10 I -3 LLJ O CD Q 1 CALIPER BULK DENSITY I DENSITY CORRECTION | kNIUM X r 3 3 9 in 19 11 g/cm 3 I -0.25 g/cm 0.25 I 9 ppm

550- -550

J

„

600- -600

650- -650

<; SITE 869

Hole 869B: Density-Porosity-Natural Gamma Ray Log Summary (continued)

SPECTRAL GAMMA RAY TOTAL POTASSIUM API units 80 -0.5 wt. % 4.5 PHOTOELECTRIC II COMPUTED NEUTRON POROSITY EFFECT THORIUM II LU Q API units LU Q CO Q CD Q I -I CALIPER BULK DENSITY DENSITY CORRECTION URANIUM n 3 3 9 i 19 1 g/cm 3 -0.25 g/cm o.25 9 ppm -1 i

700- -700

>

f

750- -750

800- -800

850- 850

370 SITE 869

Hole 869B: Geochemical Log Summary

JC SPECTRAL GAMMA RAY $ C ° a IQTAL I O ~ &§|θ API units βo I g§ x _j x _i t< I COMPUTED I POTASSIUM I URANIUM I THORIUM I £< Q «Λ IO API units 801 -0.5 wt•% 21-1 PPm g | -1 ppm g| o W

350-I 1 1 1——| • • • • Illl 1 1 1 1 1 1 1 T 350

400- .-5>• **^ y -*** -400

450- V S ^ -450

500- S '-j S ' ß -500

371 SITE 869

Hole 869B: Geochemical Log Summary (continued)

$C SPECTRAL GAMMA RAY 3 a I IQIAL II £g |θ API units 80 LU O

Q. < COMPUTED POTASSIUM URANIUM THORIUM Q<Λ 10 API units 801 -0.5 **-% 2~Ti PPm 91-1 PPm 9l Q w

• V

550- -550

600- -600

650- -650

372 SITE 869

Hole 869B: Processed Geochemical Log Summary

—i gç _i tr LLI Q LU Q O CaO & m O ££ | SiO2 | CaCO3 | FeO' | AfcO, | K2O | TiO2 | Gd | FACT | I | £ LU LU I I I I I I I I I I LU LU O<Λ 10 100l0 1Oθlθ 4θlθ 2θlθ 510 1010 PPm 5θl ICaO CaCOJ OW 350-j 1 1 1 1 . 1 1 1 1- 350

373 SITE 869

Hole 869B: Processed Geochemical Log Summary (continued)

II II LU O CaO& SiO, CaCO, FeO* K,O TiO, Gd FACT Q. < A

550- 550

600- -600

650- -650

374